diff --git a/README.md b/README.md
index ee94158..ef2d1c2 100644
--- a/README.md
+++ b/README.md
@@ -303,6 +303,27 @@ defmodule People do
 end
 ```
 
+## Configure Altnertive Credentials
+
+An index might need a different application_id / api_key. To accomplish this you can use the credentials configuration (each entry should be a `{application_id, api_key}` tuple).
+
+```elixir
+config :algoliax,
+  api_key: System.get_env("ALGOLIA_API_KEY"),
+  application_id: System.get_env("ALGOLIA_APPLICATION_ID)
+  credentials: %{
+    custom_1: {"<APPLICATION_ID_1>", "<API_KEY_2>"},
+    custom_2: {System.get_env("ALGOLIA_APPLICATION_ID_2"), System.get_env("ALGOLIA_API_KEY_2")},
+  }
+
+defmodule People do
+  use Algoliax.Indexer,
+    #....
+    credentials: :custom_1
+end
+
+If you do not specify a credentials key the default api_key / application_id on the `:algoliax` configuration will be used.
+
 ## Copyright and License
 
 Copyright (c) 2020 CORUSCANT (welcome to the jungle) - <https://www.welcometothejungle.com>
diff --git a/config/test.exs b/config/test.exs
index 58cddbf..dcbdcab 100644
--- a/config/test.exs
+++ b/config/test.exs
@@ -4,7 +4,10 @@ config :algoliax,
   application_id: "APPLICATION_ID",
   api_key: "api_key",
   batch_size: 1,
-  ecto_repos: [Algoliax.Repo]
+  ecto_repos: [Algoliax.Repo],
+  credentials: %{
+    custom_1: {"APPLICATION_ID_1", "api_key_1"}
+  }
 
 config :algoliax, Algoliax.Repo,
   pool: Ecto.Adapters.SQL.Sandbox,
diff --git a/lib/algoliax/client.ex b/lib/algoliax/client.ex
index 86629e4..4623a8e 100644
--- a/lib/algoliax/client.ex
+++ b/lib/algoliax/client.ex
@@ -3,7 +3,7 @@ defmodule Algoliax.Client do
 
   require Logger
 
-  alias Algoliax.{Config, Routes}
+  alias Algoliax.Routes
 
   def request(request, retry \\ 0)
 
@@ -17,7 +17,7 @@ defmodule Algoliax.Client do
     log(action, method, url, body)
 
     method
-    |> :hackney.request(url, request_headers(), Jason.encode!(body), [
+    |> :hackney.request(url, request_headers(request), Jason.encode!(body), [
       :with_body,
       recv_timeout: recv_timeout()
     ])
@@ -50,16 +50,16 @@ defmodule Algoliax.Client do
 
   defp build_response(response, request) do
     case Jason.decode(response) do
-      {:ok, response} -> Algoliax.Response.new(response, request[:url_params])
+      {:ok, response} -> Algoliax.Response.new(response, request)
       error -> error
     end
   end
 
-  defp request_headers do
+  defp request_headers(request) do
     [
       {"Content-type", "application/json"},
-      {"X-Algolia-API-Key", Config.api_key()},
-      {"X-Algolia-Application-Id", Config.application_id()}
+      {"X-Algolia-API-Key", request.api_key},
+      {"X-Algolia-Application-Id", request.application_id}
     ] ++ x_forwarded_for()
   end
 
diff --git a/lib/algoliax/config.ex b/lib/algoliax/config.ex
index d7d0821..729291e 100644
--- a/lib/algoliax/config.ex
+++ b/lib/algoliax/config.ex
@@ -5,10 +5,30 @@ defmodule Algoliax.Config do
     Application.get_env(:algoliax, :api_key)
   end
 
+  def api_key(credenital_name) do
+    :algoliax
+    |> Application.get_env(:credentials, [])
+    |> Map.fetch(credenital_name)
+    |> then(fn
+      {:ok, {_application_id, api_key}} -> api_key
+      :error -> raise Algoliax.InvalidAlgoliaCredentialsError, %{name: inspect(credenital_name)}
+    end)
+  end
+
   def application_id do
     Application.get_env(:algoliax, :application_id)
   end
 
+  def application_id(credenital_name) do
+    :algoliax
+    |> Application.get_env(:credentials, [])
+    |> Map.fetch(credenital_name)
+    |> then(fn
+      {:ok, {application_id, _api_key}} -> application_id
+      :error -> raise Algoliax.InvalidAlgoliaCredentialsError, %{name: inspect(credenital_name)}
+    end)
+  end
+
   def cursor_field do
     Application.get_env(:algoliax, :cursor_field)
   end
diff --git a/lib/algoliax/exceptions.ex b/lib/algoliax/exceptions.ex
index 290be4b..3b2691c 100644
--- a/lib/algoliax/exceptions.ex
+++ b/lib/algoliax/exceptions.ex
@@ -44,6 +44,19 @@ defmodule Algoliax.InvalidAlgoliaSettingsFunctionError do
   end
 end
 
+defmodule Algoliax.InvalidAlgoliaCredentialsError do
+  @moduledoc "Raise when `:crendentials` are invalid"
+
+  defexception [:message]
+
+  @impl true
+  def exception(%{name: name}) do
+    %__MODULE__{
+      message: "Expected #{name} to be configuired in alogila credentials"
+    }
+  end
+end
+
 defmodule Algoliax.InvalidAlgoliaSettingsConfigurationError do
   @moduledoc "Raise when the `:algolia` settings are unsupported"
 
diff --git a/lib/algoliax/indexer.ex b/lib/algoliax/indexer.ex
index 26077ad..684e46d 100644
--- a/lib/algoliax/indexer.ex
+++ b/lib/algoliax/indexer.ex
@@ -10,6 +10,7 @@ defmodule Algoliax.Indexer do
   - `:schemas`: Specify which schemas used to populate index, Default: `[__CALLER__]`
   - `:default_filters`: Specify default filters to be used when reindex without providing a query. Must be a map or a function name (that returns a map). Default: `%{}`.
   - `:algolia`: Any valid Algolia settings (using snake case or camel case, ie `attributeForFaceting` can be configured with `:attribute_for_faceting`) or the name of 0-arity function that returns those settings.
+  - `:credentials`: Specify an alternative application_id / api_key for this index. Default `nil`
 
   On first call to Algolia, we check that the settings on Algolia are up to date.
 
@@ -157,6 +158,29 @@ defmodule Algoliax.Indexer do
       [attribute_for_faceting: ["age"]]
     end
   end
+
+  ### Alternative Credentials
+
+  An index might need a different application_id / api_key. To accomplish this you can use the credentials configuration.
+
+  ```elixir
+  config :algoliax,
+    api_key: System.get_env("ALGOLIA_API_KEY"),
+    application_id: System.get_env("ALGOLIA_APPLICATION_ID)
+    credentials: %{
+      custom_1: {"<APPLICATION_ID_1>", "<API_KEY_2>"},
+      custom_2: {System.get_env("ALGOLIA_APPLICATION_ID_2"), System.get_env("ALGOLIA_API_KEY_2")},
+    }
+
+  defmodule People do
+    use Algoliax.Indexer,
+      #....
+      credentials: :custom_1
+  end
+
+  If you do not specify a credentials key the default api_key / application_id on the `:algoliax` configuration will be used.
+  ```
+
   """
 
   alias Algoliax.Resources.{Index, Object, Search}
@@ -347,7 +371,7 @@ defmodule Algoliax.Indexer do
     > NOTE: filters as Map supports only `:where` and equality
     """
     @callback reindex(query :: Ecto.Query.t(), opts :: Keyword.t()) ::
-                {:ok, [Algoliax.Response.t()]} | {:ok, list(Algoliax.Responses.t())}
+                {:ok, [{:ok, Algoliax.Response.t()}]} | {:ok, list(Algoliax.Responses.t())}
 
     @doc """
     Reindex all objects ([Ecto](https://hexdocs.pm/ecto/Ecto.html) specific)
@@ -361,7 +385,7 @@ defmodule Algoliax.Indexer do
     - `:force_delete`: delete objects where `to_be_indexed?` is `false`
     """
     @callback reindex(opts :: Keyword.t()) ::
-                {:ok, [Algoliax.Response.t()]} | {:ok, list(Algoliax.Responses.t())}
+                {:ok, [{:ok, Algoliax.Response.t()}]} | {:ok, list(Algoliax.Responses.t())}
 
     @doc """
     Reindex atomically ([Ecto](https://hexdocs.pm/ecto/Ecto.html) specific)
diff --git a/lib/algoliax/resources/index.ex b/lib/algoliax/resources/index.ex
index 0f60c32..d3b3e9f 100644
--- a/lib/algoliax/resources/index.ex
+++ b/lib/algoliax/resources/index.ex
@@ -1,9 +1,17 @@
 defmodule Algoliax.Resources.Index do
   @moduledoc false
 
-  import Algoliax.Utils, only: [index_name: 2, algolia_settings: 2, render_response: 1]
   import Algoliax.Client, only: [request: 1]
 
+  import Algoliax.Utils,
+    only: [
+      algolia_settings: 2,
+      api_key: 1,
+      application_id: 1,
+      index_name: 2,
+      render_response: 1
+    ]
+
   alias Algoliax.{Settings, SettingsStore}
 
   def ensure_settings(module, index_name, settings, replica_index) do
@@ -11,10 +19,11 @@ defmodule Algoliax.Resources.Index do
       nil ->
         request_configure_index(
           index_name,
+          settings,
           settings_to_algolia_settings(module, settings, replica_index)
         )
 
-        algolia_remote_settings = request_get_settings(index_name)
+        algolia_remote_settings = request_get_settings(index_name, settings)
         SettingsStore.set_settings(index_name, algolia_remote_settings)
         replicas_names(module, settings, replica_index)
 
@@ -94,7 +103,7 @@ defmodule Algoliax.Resources.Index do
   def get_settings(module, settings) do
     index_name(module, settings)
     |> Enum.map(fn index_name ->
-      algolia_remote_settings = request_get_settings(index_name)
+      algolia_remote_settings = request_get_settings(index_name, settings)
       SettingsStore.set_settings(index_name, algolia_remote_settings)
       algolia_remote_settings
     end)
@@ -108,6 +117,7 @@ defmodule Algoliax.Resources.Index do
       r =
         request_configure_index(
           index_name,
+          settings,
           settings_to_algolia_settings(module, settings, replica_index)
         )
 
@@ -125,25 +135,43 @@ defmodule Algoliax.Resources.Index do
     end)
   end
 
-  defp request_configure_index(index_name, settings) do
+  defp request_configure_index(index_name, settings, alogolia_settings) do
+    api_key = api_key(settings)
+    application_id = application_id(settings)
+
     request(%{
       action: :configure_index,
-      url_params: [index_name: index_name],
-      body: settings
+      url_params: [index_name: index_name, application_id: application_id],
+      body: alogolia_settings,
+      api_key: api_key,
+      application_id: application_id
     })
   end
 
-  defp request_get_settings(index_name) do
+  defp request_get_settings(index_name, settings) do
+    api_key = api_key(settings)
+    application_id = application_id(settings)
+
     request(%{
       action: :get_settings,
-      url_params: [index_name: index_name]
+      url_params: [index_name: index_name, application_id: application_id],
+      api_key: api_key,
+      application_id: application_id
     })
   end
 
   def delete_index(module, settings) do
+    api_key = api_key(settings)
+    application_id = application_id(settings)
+
     index_name(module, settings)
     |> Enum.map(fn index_name ->
-      request(%{action: :delete_index, url_params: [index_name: index_name]})
+      request(%{
+        action: :delete_index,
+        url_params: [index_name: index_name, application_id: application_id],
+        api_key: api_key,
+        application_id: application_id
+      })
     end)
     |> render_response()
   end
diff --git a/lib/algoliax/resources/object.ex b/lib/algoliax/resources/object.ex
index ead9ea7..81cfe26 100644
--- a/lib/algoliax/resources/object.ex
+++ b/lib/algoliax/resources/object.ex
@@ -1,26 +1,43 @@
 defmodule Algoliax.Resources.Object do
   @moduledoc false
 
-  import Algoliax.Utils, only: [index_name: 2, object_id_attribute: 1, render_response: 1]
   import Algoliax.Client, only: [request: 1]
 
+  import Algoliax.Utils,
+    only: [
+      api_key: 1,
+      application_id: 1,
+      index_name: 2,
+      object_id_attribute: 1,
+      render_response: 1
+    ]
+
   alias Algoliax.TemporaryIndexer
 
   def get_object(module, settings, model) do
+    api_key = api_key(settings)
+    application_id = application_id(settings)
+
     index_name(module, settings)
     |> Enum.map(fn index_name ->
       request(%{
         action: :get_object,
         url_params: [
           index_name: index_name,
-          object_id: get_object_id(module, settings, model)
-        ]
+          object_id: get_object_id(module, settings, model),
+          application_id: application_id
+        ],
+        api_key: api_key,
+        application_id: application_id
       })
     end)
     |> render_response()
   end
 
   def save_objects(module, settings, models, opts) do
+    api_key = api_key(settings)
+    application_id = application_id(settings)
+
     objects =
       index_name(module, settings)
       |> Enum.reduce(%{}, fn index_name, acc ->
@@ -36,8 +53,13 @@ defmodule Algoliax.Resources.Object do
       |> Enum.map(fn {index_name, objects} ->
         request(%{
           action: :save_objects,
-          url_params: [index_name: index_name],
-          body: %{requests: objects}
+          url_params: [
+            index_name: index_name,
+            application_id: application_id
+          ],
+          body: %{requests: objects},
+          api_key: api_key,
+          application_id: application_id
         })
       end)
       |> render_response()
@@ -65,13 +87,22 @@ defmodule Algoliax.Resources.Object do
 
   defp save_object(module, settings, model, index_name) do
     if apply(module, :to_be_indexed?, [model]) do
+      api_key = api_key(settings)
+      application_id = application_id(settings)
+
       object = build_object(module, settings, model, index_name)
       call_indexer(:save_object, module, settings, model)
 
       request(%{
         action: :save_object,
-        url_params: [index_name: index_name, object_id: object.objectID],
-        body: object
+        url_params: [
+          index_name: index_name,
+          object_id: object.objectID,
+          application_id: application_id
+        ],
+        body: object,
+        api_key: api_key,
+        application_id: application_id
       })
     else
       {:not_indexable, model}
@@ -79,6 +110,9 @@ defmodule Algoliax.Resources.Object do
   end
 
   def delete_object(module, settings, model) do
+    api_key = api_key(settings)
+    application_id = application_id(settings)
+
     call_indexer(:delete_object, module, settings, model)
 
     index_name(module, settings)
@@ -87,14 +121,20 @@ defmodule Algoliax.Resources.Object do
         action: :delete_object,
         url_params: [
           index_name: index_name,
-          object_id: get_object_id(module, settings, model)
-        ]
+          object_id: get_object_id(module, settings, model),
+          application_id: application_id
+        ],
+        api_key: api_key,
+        application_id: application_id
       })
     end)
     |> render_response()
   end
 
   def delete_by(module, settings, matching_filter) do
+    api_key = api_key(settings)
+    application_id = application_id(settings)
+
     call_indexer(:delete_by, module, settings, matching_filter)
 
     body =
@@ -111,9 +151,12 @@ defmodule Algoliax.Resources.Object do
       request(%{
         action: :delete_by,
         url_params: [
-          index_name: index_name
+          index_name: index_name,
+          application_id: application_id
         ],
-        body: body
+        body: body,
+        api_key: api_key,
+        application_id: application_id
       })
     end)
     |> render_response()
diff --git a/lib/algoliax/resources/object_ecto.ex b/lib/algoliax/resources/object_ecto.ex
index 943cb3b..6f08cc8 100644
--- a/lib/algoliax/resources/object_ecto.ex
+++ b/lib/algoliax/resources/object_ecto.ex
@@ -4,7 +4,15 @@ if Code.ensure_loaded?(Ecto) do
 
     import Ecto.Query
     import Algoliax.Client, only: [request: 1]
-    import Algoliax.Utils, only: [index_name: 2, schemas: 2, default_filters: 2]
+
+    import Algoliax.Utils,
+      only: [
+        api_key: 1,
+        application_id: 1,
+        default_filters: 2,
+        index_name: 2,
+        schemas: 2
+      ]
 
     alias Algoliax.Resources.Object
 
@@ -77,6 +85,9 @@ if Code.ensure_loaded?(Ecto) do
 
     # sobelow_skip ["DOS.BinToAtom"]
     def reindex_atomic(module, settings) do
+      api_key = api_key(settings)
+      application_id = application_id(settings)
+
       Algoliax.UtilsEcto.repo(settings)
 
       index_name(module, settings)
@@ -93,11 +104,16 @@ if Code.ensure_loaded?(Ecto) do
 
           request(%{
             action: :move_index,
-            url_params: [index_name: tmp_index_name],
+            url_params: [
+              index_name: tmp_index_name,
+              application_id: application_id
+            ],
             body: %{
               operation: "move",
               destination: "#{index_name}"
-            }
+            },
+            api_key: api_key,
+            application_id: application_id
           })
 
           {:ok, :completed}
diff --git a/lib/algoliax/resources/search.ex b/lib/algoliax/resources/search.ex
index 6b9fbda..f12750a 100644
--- a/lib/algoliax/resources/search.ex
+++ b/lib/algoliax/resources/search.ex
@@ -1,9 +1,21 @@
 defmodule Algoliax.Resources.Search do
   @moduledoc false
-  import Algoliax.Utils, only: [index_name: 2, camelize: 1, render_response: 1]
+
   import Algoliax.Client, only: [request: 1]
 
+  import Algoliax.Utils,
+    only: [
+      api_key: 1,
+      application_id: 1,
+      camelize: 1,
+      index_name: 2,
+      render_response: 1
+    ]
+
   def search(module, settings, query, params) do
+    api_key = api_key(settings)
+    application_id = application_id(settings)
+
     index_name(module, settings)
     |> Enum.map(fn index_name ->
       body =
@@ -14,14 +26,22 @@ defmodule Algoliax.Resources.Search do
 
       request(%{
         action: :search,
-        url_params: [index_name: index_name],
-        body: body
+        url_params: [
+          index_name: index_name,
+          application_id: application_id
+        ],
+        body: body,
+        api_key: api_key,
+        application_id: application_id
       })
     end)
     |> render_response()
   end
 
   def search_facet(module, settings, facet_name, facet_query, params) do
+    api_key = api_key(settings)
+    application_id = application_id(settings)
+
     index_name(module, settings)
     |> Enum.map(fn index_name ->
       body =
@@ -36,8 +56,14 @@ defmodule Algoliax.Resources.Search do
 
       request(%{
         action: :search_facet,
-        url_params: [index_name: index_name, facet_name: facet_name],
-        body: body
+        url_params: [
+          index_name: index_name,
+          facet_name: facet_name,
+          application_id: application_id
+        ],
+        body: body,
+        api_key: api_key,
+        application_id: application_id
       })
     end)
     |> render_response()
diff --git a/lib/algoliax/resources/task.ex b/lib/algoliax/resources/task.ex
index f50b4e5..f882158 100644
--- a/lib/algoliax/resources/task.ex
+++ b/lib/algoliax/resources/task.ex
@@ -10,8 +10,11 @@ defmodule Algoliax.Resources.Task do
       action: :task,
       url_params: [
         index_name: index_name,
-        task_id: response.task_id
-      ]
+        task_id: response.task_id,
+        application_id: response.application_id
+      ],
+      api_key: response.api_key,
+      application_id: response.application_id
     })
   end
 end
diff --git a/lib/algoliax/response.ex b/lib/algoliax/response.ex
index ac5d4da..164b3c2 100644
--- a/lib/algoliax/response.ex
+++ b/lib/algoliax/response.ex
@@ -4,20 +4,31 @@ defmodule Algoliax.Response do
   """
 
   @type t :: %__MODULE__{
+          api_key: binary(),
+          application_id: binary(),
+          params: keyword(),
           response: map(),
-          task_id: integer(),
-          updated_at: binary(),
-          params: keyword()
+          task_id: integer() | nil,
+          updated_at: binary() | nil
         }
 
-  defstruct [:response, :task_id, :updated_at, :params]
+  defstruct [
+    :api_key,
+    :application_id,
+    :params,
+    :response,
+    :task_id,
+    :updated_at
+  ]
 
-  def new(response, params) do
+  def new(response, request) do
     response = %__MODULE__{
+      api_key: request.api_key,
+      application_id: request.application_id,
+      params: request.url_params,
       response: response,
       task_id: response["taskID"],
-      updated_at: response["updatedAt"],
-      params: params
+      updated_at: response["updatedAt"]
     }
 
     {:ok, response}
diff --git a/lib/algoliax/routes.ex b/lib/algoliax/routes.ex
index cb2e6e1..30cc63b 100644
--- a/lib/algoliax/routes.ex
+++ b/lib/algoliax/routes.ex
@@ -1,6 +1,5 @@
 defmodule Algoliax.Routes do
   @moduledoc false
-  alias Algoliax.Config
 
   @paths %{
     search: {"/{index_name}/query", :post},
@@ -23,14 +22,15 @@ defmodule Algoliax.Routes do
       |> Map.get(action)
 
     url =
-      action_path
-      |> build_path(url_params)
-      |> build_url(method, retry)
+      method
+      |> build_url(retry)
+      |> Kernel.<>(action_path)
+      |> interpolate_path(url_params)
 
     {method, url}
   end
 
-  defp build_path(path, args) do
+  defp interpolate_path(path, args) do
     args
     |> Keyword.keys()
     |> Enum.reduce(path, fn key, path ->
@@ -39,51 +39,45 @@ defmodule Algoliax.Routes do
     end)
   end
 
-  defp build_url(path, :get, 0) do
+  defp build_url(:get, 0) do
     url_read()
-    |> String.replace(~r/{{application_id}}/, Config.application_id())
-    |> Kernel.<>(path)
   end
 
-  defp build_url(path, _method, 0) do
+  defp build_url(_method, 0) do
     url_write()
-    |> String.replace(~r/{{application_id}}/, Config.application_id())
-    |> Kernel.<>(path)
   end
 
-  defp build_url(path, _method, retry) do
+  defp build_url(_method, retry) do
     url_retry()
-    |> String.replace(~r/{{application_id}}/, Config.application_id())
     |> String.replace(~r/{{retry}}/, to_string(retry))
-    |> Kernel.<>(path)
   end
 
   if Mix.env() == :test do
     defp url_read do
       port = Application.get_env(:algoliax, :mock_api_port)
-      "http://localhost:#{port}/{{application_id}}/read"
+      "http://localhost:#{port}/{application_id}/read"
     end
 
     defp url_write do
       port = Application.get_env(:algoliax, :mock_api_port)
-      "http://localhost:#{port}/{{application_id}}/write"
+      "http://localhost:#{port}/{application_id}/write"
     end
 
     defp url_retry do
       port = Application.get_env(:algoliax, :mock_api_port)
-      "http://localhost:#{port}/{{application_id}}/retry/{{retry}}"
+      "http://localhost:#{port}/{application_id}/retry/{{retry}}"
     end
   else
     defp url_read do
-      "https://{{application_id}}-dsn.algolia.net/1/indexes"
+      "https://{application_id}-dsn.algolia.net/1/indexes"
     end
 
     defp url_write do
-      "https://{{application_id}}.algolia.net/1/indexes"
+      "https://{application_id}.algolia.net/1/indexes"
     end
 
     defp url_retry do
-      "https://{{application_id}}-{{retry}}.algolianet.com/1/indexes"
+      "https://{application_id}-{{retry}}.algolianet.com/1/indexes"
     end
   end
 end
diff --git a/lib/algoliax/utils.ex b/lib/algoliax/utils.ex
index 5d07c26..9658bc8 100644
--- a/lib/algoliax/utils.ex
+++ b/lib/algoliax/utils.ex
@@ -1,8 +1,31 @@
 defmodule Algoliax.Utils do
   @moduledoc false
 
+  alias Algoliax.Config
   alias Algoliax.Resources.Index
 
+  @spec api_key(keyword()) :: binary()
+  def api_key(settings) do
+    case Keyword.get(settings, :credentials) do
+      nil ->
+        Config.api_key()
+
+      atom when is_atom(atom) ->
+        Config.api_key(atom)
+    end
+  end
+
+  @spec application_id(keyword()) :: binary()
+  def application_id(settings) do
+    case Keyword.get(settings, :credentials) do
+      nil ->
+        Config.application_id()
+
+      atom when is_atom(atom) ->
+        Config.application_id(atom)
+    end
+  end
+
   def index_name(module, settings) do
     indexes =
       case Keyword.get(settings, :index_name) do
diff --git a/test/algoliax/client_test.exs b/test/algoliax/client_test.exs
index cae57d5..a02b902 100644
--- a/test/algoliax/client_test.exs
+++ b/test/algoliax/client_test.exs
@@ -2,10 +2,20 @@ defmodule Algoliax.ClientTest do
   use Algoliax.RequestCase
 
   test "test retries" do
-    Application.put_env(:algoliax, :api_key, "api_key")
+    api_key = "api_key"
+    application_id = "APPLICATION_ID"
 
     Algoliax.Client.request(
-      %{action: :get_object, url_params: [index_name: :index_name, object_id: "error"]},
+      %{
+        action: :get_object,
+        api_key: api_key,
+        application_id: application_id,
+        url_params: [
+          application_id: application_id,
+          index_name: :index_name,
+          object_id: "error"
+        ]
+      },
       0
     )
 
@@ -16,7 +26,8 @@ defmodule Algoliax.ClientTest do
   end
 
   test "Error http" do
-    Application.put_env(:algoliax, :api_key, "api_key_invalid")
+    api_key = "api_key_invalid"
+    application_id = "APPLICATION_ID"
 
     message = """
     Algolia HTTP error:
@@ -28,7 +39,13 @@ defmodule Algoliax.ClientTest do
       Algoliax.Client.request(
         %{
           action: :get_object,
-          url_params: [index_name: :index_name_not_authorized, object_id: "Whatever"]
+          api_key: api_key,
+          application_id: application_id,
+          url_params: [
+            application_id: application_id,
+            index_name: :index_name_not_authorized,
+            object_id: "Whatever"
+          ]
         },
         0
       )
diff --git a/test/algoliax/replica_test.exs b/test/algoliax/replica_test.exs
index 20dc737..4660ee6 100644
--- a/test/algoliax/replica_test.exs
+++ b/test/algoliax/replica_test.exs
@@ -5,6 +5,9 @@ defmodule AlgoliaxTest.ReplicaTest do
   alias Algoliax.Schemas.PeopleWithReplicasMultipleIndexes
   alias Algoliax.Schemas.PeopleWithInvalidReplicas
 
+  @application_id "APPLICATION_ID"
+  @api_key "api_key"
+
   setup do
     Algoliax.SettingsStore.set_settings(:algoliax_people_replicas, %{})
     Algoliax.SettingsStore.set_settings(:algoliax_people_replicas_en, %{})
@@ -56,7 +59,12 @@ defmodule AlgoliaxTest.ReplicaTest do
                  {:ok,
                   %Algoliax.Response{
                     response: %{"taskID" => _, "updatedAt" => _},
-                    params: [index_name: :algoliax_people_replicas_en]
+                    params: [
+                      index_name: :algoliax_people_replicas_en,
+                      application_id: @application_id
+                    ],
+                    application_id: @application_id,
+                    api_key: @api_key
                   }}
                ]
              } = res
@@ -67,7 +75,12 @@ defmodule AlgoliaxTest.ReplicaTest do
                  {:ok,
                   %Algoliax.Response{
                     response: %{"taskID" => _, "updatedAt" => _},
-                    params: [index_name: :algoliax_people_replicas_fr]
+                    params: [
+                      index_name: :algoliax_people_replicas_fr,
+                      application_id: @application_id
+                    ],
+                    application_id: @application_id,
+                    api_key: @api_key
                   }}
                ]
              } = res2
@@ -200,7 +213,11 @@ defmodule AlgoliaxTest.ReplicaTest do
                  {:ok,
                   %Algoliax.Response{
                     response: %{"taskID" => _, "updatedAt" => _, "objectID" => ^reference},
-                    params: [index_name: :algoliax_people_replicas_en, object_id: ^reference]
+                    params: [
+                      index_name: :algoliax_people_replicas_en,
+                      object_id: ^reference,
+                      application_id: @application_id
+                    ]
                   }}
                ]
              } = res
@@ -211,7 +228,11 @@ defmodule AlgoliaxTest.ReplicaTest do
                  {:ok,
                   %Algoliax.Response{
                     response: %{"taskID" => _, "updatedAt" => _, "objectID" => ^reference},
-                    params: [index_name: :algoliax_people_replicas_fr, object_id: ^reference]
+                    params: [
+                      index_name: :algoliax_people_replicas_fr,
+                      object_id: ^reference,
+                      application_id: @application_id
+                    ]
                   }}
                ]
              } = res2
@@ -301,7 +322,12 @@ defmodule AlgoliaxTest.ReplicaTest do
                       "taskID" => _,
                       "objectIDs" => [^reference1, ^reference2]
                     },
-                    params: [index_name: :algoliax_people_replicas_en]
+                    params: [
+                      index_name: :algoliax_people_replicas_en,
+                      application_id: @application_id
+                    ],
+                    application_id: @application_id,
+                    api_key: @api_key
                   }}
                ]
              } = res
@@ -315,7 +341,12 @@ defmodule AlgoliaxTest.ReplicaTest do
                       "taskID" => _,
                       "objectIDs" => [^reference1, ^reference2]
                     },
-                    params: [index_name: :algoliax_people_replicas_fr]
+                    params: [
+                      index_name: :algoliax_people_replicas_fr,
+                      application_id: @application_id
+                    ],
+                    application_id: @application_id,
+                    api_key: @api_key
                   }}
                ]
              } = res2
@@ -370,7 +401,13 @@ defmodule AlgoliaxTest.ReplicaTest do
                  {:ok,
                   %Algoliax.Response{
                     response: %{"objectID" => "known"},
-                    params: [index_name: :algoliax_people_replicas_en, object_id: "known"]
+                    params: [
+                      index_name: :algoliax_people_replicas_en,
+                      object_id: "known",
+                      application_id: @application_id
+                    ],
+                    application_id: @application_id,
+                    api_key: @api_key
                   }}
                ]
              } = res
@@ -381,7 +418,13 @@ defmodule AlgoliaxTest.ReplicaTest do
                  {:ok,
                   %Algoliax.Response{
                     response: %{"objectID" => "known"},
-                    params: [index_name: :algoliax_people_replicas_fr, object_id: "known"]
+                    params: [
+                      index_name: :algoliax_people_replicas_fr,
+                      object_id: "known",
+                      application_id: @application_id
+                    ],
+                    application_id: @application_id,
+                    api_key: @api_key
                   }}
                ]
              } = res2
@@ -486,7 +529,12 @@ defmodule AlgoliaxTest.ReplicaTest do
                  {:ok,
                   %Algoliax.Response{
                     response: %{"searchableAttributes" => ["test"]},
-                    params: [index_name: :algoliax_people_replicas_en]
+                    params: [
+                      index_name: :algoliax_people_replicas_en,
+                      application_id: @application_id
+                    ],
+                    application_id: @application_id,
+                    api_key: @api_key
                   }}
                ]
              } = res
@@ -497,7 +545,12 @@ defmodule AlgoliaxTest.ReplicaTest do
                  {:ok,
                   %Algoliax.Response{
                     response: %{"searchableAttributes" => ["test"]},
-                    params: [index_name: :algoliax_people_replicas_fr]
+                    params: [
+                      index_name: :algoliax_people_replicas_fr,
+                      application_id: @application_id
+                    ],
+                    application_id: @application_id,
+                    api_key: @api_key
                   }}
                ]
              } = res2
diff --git a/test/algoliax/routes_test.exs b/test/algoliax/routes_test.exs
index 839f15e..5edfa1c 100644
--- a/test/algoliax/routes_test.exs
+++ b/test/algoliax/routes_test.exs
@@ -4,10 +4,9 @@ defmodule Algoliax.RoutesTest do
   alias Algoliax.Routes
 
   @index_name :algolia_index
+  @application_id "APPLICATION_ID"
 
   setup do
-    Application.put_env(:algoliax, :application_id, "APPLICATION_ID")
-
     people = %{objectID: 10}
 
     {:ok, %{people: people}}
@@ -15,84 +14,127 @@ defmodule Algoliax.RoutesTest do
 
   describe "First attempts" do
     test "url delete_index" do
-      assert Routes.url(:delete_index, index_name: @index_name) ==
+      assert Routes.url(:delete_index, application_id: @application_id, index_name: @index_name) ==
                {:delete, "http://localhost:8002/APPLICATION_ID/write/algolia_index"}
     end
 
     test "url get_settings" do
-      assert Routes.url(:get_settings, index_name: @index_name) ==
+      assert Routes.url(:get_settings, application_id: @application_id, index_name: @index_name) ==
                {:get, "http://localhost:8002/APPLICATION_ID/read/algolia_index/settings"}
     end
 
     test "url configure_index" do
-      assert Routes.url(:configure_index, index_name: @index_name) ==
+      assert Routes.url(:configure_index,
+               application_id: @application_id,
+               index_name: @index_name
+             ) ==
                {:put, "http://localhost:8002/APPLICATION_ID/write/algolia_index/settings"}
     end
 
     test "url save_objects" do
-      assert Routes.url(:save_objects, index_name: @index_name) ==
+      assert Routes.url(:save_objects, application_id: @application_id, index_name: @index_name) ==
                {:post, "http://localhost:8002/APPLICATION_ID/write/algolia_index/batch"}
     end
 
     test "url get_object" do
-      assert Routes.url(:get_object, index_name: @index_name, object_id: 10) ==
+      assert Routes.url(:get_object,
+               application_id: @application_id,
+               index_name: @index_name,
+               object_id: 10
+             ) ==
                {:get, "http://localhost:8002/APPLICATION_ID/read/algolia_index/10"}
     end
 
     test "url save_object" do
-      assert Routes.url(:save_object, index_name: @index_name, object_id: 10) ==
+      assert Routes.url(:save_object,
+               application_id: @application_id,
+               index_name: @index_name,
+               object_id: 10
+             ) ==
                {:put, "http://localhost:8002/APPLICATION_ID/write/algolia_index/10"}
     end
 
     test "url delete_object" do
-      assert Routes.url(:delete_object, index_name: @index_name, object_id: 10) ==
+      assert Routes.url(:delete_object,
+               application_id: @application_id,
+               index_name: @index_name,
+               object_id: 10
+             ) ==
                {:delete, "http://localhost:8002/APPLICATION_ID/write/algolia_index/10"}
     end
 
     test "url delete_by" do
-      assert Routes.url(:delete_by, index_name: @index_name) ==
+      assert Routes.url(:delete_by, application_id: @application_id, index_name: @index_name) ==
                {:post, "http://localhost:8002/APPLICATION_ID/write/algolia_index/deleteByQuery"}
     end
   end
 
   describe "First retry" do
     test "url delete_index" do
-      assert Routes.url(:delete_index, [index_name: @index_name], 1) ==
+      assert Routes.url(
+               :delete_index,
+               [application_id: @application_id, index_name: @index_name],
+               1
+             ) ==
                {:delete, "http://localhost:8002/APPLICATION_ID/retry/1/algolia_index"}
     end
 
     test "url get_settings" do
-      assert Routes.url(:get_settings, [index_name: @index_name], 1) ==
+      assert Routes.url(
+               :get_settings,
+               [application_id: @application_id, index_name: @index_name],
+               1
+             ) ==
                {:get, "http://localhost:8002/APPLICATION_ID/retry/1/algolia_index/settings"}
     end
 
     test "url configure_index" do
-      assert Routes.url(:configure_index, [index_name: @index_name], 1) ==
+      assert Routes.url(
+               :configure_index,
+               [application_id: @application_id, index_name: @index_name],
+               1
+             ) ==
                {:put, "http://localhost:8002/APPLICATION_ID/retry/1/algolia_index/settings"}
     end
 
     test "url save_objects" do
-      assert Routes.url(:save_objects, [index_name: @index_name], 1) ==
+      assert Routes.url(
+               :save_objects,
+               [application_id: @application_id, index_name: @index_name],
+               1
+             ) ==
                {:post, "http://localhost:8002/APPLICATION_ID/retry/1/algolia_index/batch"}
     end
 
     test "url get_object" do
-      assert Routes.url(:get_object, [index_name: @index_name, object_id: 10], 1) ==
+      assert Routes.url(
+               :get_object,
+               [application_id: @application_id, index_name: @index_name, object_id: 10],
+               1
+             ) ==
                {:get, "http://localhost:8002/APPLICATION_ID/retry/1/algolia_index/10"}
     end
 
     test "url save_object" do
-      assert Routes.url(:save_object, [index_name: @index_name, object_id: 10], 1) ==
+      assert Routes.url(
+               :save_object,
+               [application_id: @application_id, index_name: @index_name, object_id: 10],
+               1
+             ) ==
                {:put, "http://localhost:8002/APPLICATION_ID/retry/1/algolia_index/10"}
     end
 
     test "url delete_object" do
-      assert Routes.url(:delete_object, [index_name: @index_name, object_id: 10], 1) ==
+      assert Routes.url(
+               :delete_object,
+               [application_id: @application_id, index_name: @index_name, object_id: 10],
+               1
+             ) ==
                {:delete, "http://localhost:8002/APPLICATION_ID/retry/1/algolia_index/10"}
     end
 
     test "url delete_by" do
-      assert Routes.url(:delete_by, [index_name: @index_name], 1) ==
+      assert Routes.url(:delete_by, [application_id: @application_id, index_name: @index_name], 1) ==
                {:post, "http://localhost:8002/APPLICATION_ID/retry/1/algolia_index/deleteByQuery"}
     end
   end
diff --git a/test/algoliax/struct_test.exs b/test/algoliax/struct_test.exs
index 4a7e975..e69398a 100644
--- a/test/algoliax/struct_test.exs
+++ b/test/algoliax/struct_test.exs
@@ -4,10 +4,14 @@ defmodule AlgoliaxTest.StructTest do
   alias Algoliax.Schemas.{
     PeopleStruct,
     PeopleStructMultipleIndexes,
-    PeopleStructRuntimeMultipleIndexes,
-    PeopleStructRuntimeIndexName
+    PeopleStructCredentials,
+    PeopleStructRuntimeIndexName,
+    PeopleStructRuntimeMultipleIndexes
   }
 
+  @application_id "APPLICATION_ID"
+  @api_key "api_key"
+
   setup do
     Algoliax.SettingsStore.set_settings(:algoliax_people_struct, %{})
     Algoliax.SettingsStore.set_settings(:algoliax_people_with_prepare_object_struct, %{})
@@ -171,7 +175,12 @@ defmodule AlgoliaxTest.StructTest do
                  {:ok,
                   %Algoliax.Response{
                     response: %{"taskID" => _, "updatedAt" => _},
-                    params: [index_name: :algoliax_people_struct_en]
+                    params: [
+                      index_name: :algoliax_people_struct_en,
+                      application_id: @application_id
+                    ],
+                    application_id: @application_id,
+                    api_key: @api_key
                   }}
                ]
              } = res
@@ -182,7 +191,12 @@ defmodule AlgoliaxTest.StructTest do
                  {:ok,
                   %Algoliax.Response{
                     response: %{"taskID" => _, "updatedAt" => _},
-                    params: [index_name: :algoliax_people_struct_fr]
+                    params: [
+                      index_name: :algoliax_people_struct_fr,
+                      application_id: @application_id
+                    ],
+                    application_id: @application_id,
+                    api_key: @api_key
                   }}
                ]
              } = res2
@@ -222,7 +236,13 @@ defmodule AlgoliaxTest.StructTest do
                  {:ok,
                   %Algoliax.Response{
                     response: %{"objectID" => ^reference, "taskID" => _, "updatedAt" => _},
-                    params: [index_name: :algoliax_people_struct_en, object_id: ^reference]
+                    params: [
+                      index_name: :algoliax_people_struct_en,
+                      object_id: ^reference,
+                      application_id: @application_id
+                    ],
+                    application_id: @application_id,
+                    api_key: @api_key
                   }}
                ]
              } = res
@@ -233,7 +253,13 @@ defmodule AlgoliaxTest.StructTest do
                  {:ok,
                   %Algoliax.Response{
                     response: %{"objectID" => ^reference, "taskID" => _, "updatedAt" => _},
-                    params: [index_name: :algoliax_people_struct_fr, object_id: ^reference]
+                    params: [
+                      index_name: :algoliax_people_struct_fr,
+                      object_id: ^reference,
+                      application_id: @application_id
+                    ],
+                    application_id: @application_id,
+                    api_key: @api_key
                   }}
                ]
              } = res2
@@ -292,7 +318,12 @@ defmodule AlgoliaxTest.StructTest do
                  {:ok,
                   %Algoliax.Response{
                     response: %{"taskID" => _, "objectIDs" => [^reference1]},
-                    params: [index_name: :algoliax_people_struct_en]
+                    params: [
+                      index_name: :algoliax_people_struct_en,
+                      application_id: @application_id
+                    ],
+                    application_id: @application_id,
+                    api_key: @api_key
                   }}
                ]
              } = res
@@ -303,7 +334,12 @@ defmodule AlgoliaxTest.StructTest do
                  {:ok,
                   %Algoliax.Response{
                     response: %{"taskID" => _, "objectIDs" => [^reference1]},
-                    params: [index_name: :algoliax_people_struct_fr]
+                    params: [
+                      index_name: :algoliax_people_struct_fr,
+                      application_id: @application_id
+                    ],
+                    application_id: @application_id,
+                    api_key: @api_key
                   }}
                ]
              } = res2
@@ -351,7 +387,12 @@ defmodule AlgoliaxTest.StructTest do
                  {:ok,
                   %Algoliax.Response{
                     response: %{"taskID" => _, "objectIDs" => [^reference1, ^reference2]},
-                    params: [index_name: :algoliax_people_struct_en]
+                    params: [
+                      index_name: :algoliax_people_struct_en,
+                      application_id: @application_id
+                    ],
+                    application_id: @application_id,
+                    api_key: @api_key
                   }}
                ]
              } = res
@@ -362,7 +403,12 @@ defmodule AlgoliaxTest.StructTest do
                  {:ok,
                   %Algoliax.Response{
                     response: %{"taskID" => _, "objectIDs" => [^reference1, ^reference2]},
-                    params: [index_name: :algoliax_people_struct_fr]
+                    params: [
+                      index_name: :algoliax_people_struct_fr,
+                      application_id: @application_id
+                    ],
+                    application_id: @application_id,
+                    api_key: @api_key
                   }}
                ]
              } = res2
@@ -404,7 +450,13 @@ defmodule AlgoliaxTest.StructTest do
                  {:ok,
                   %Algoliax.Response{
                     response: %{"objectID" => "known"},
-                    params: [index_name: :algoliax_people_struct_en, object_id: "known"]
+                    params: [
+                      index_name: :algoliax_people_struct_en,
+                      object_id: "known",
+                      application_id: @application_id
+                    ],
+                    application_id: @application_id,
+                    api_key: @api_key
                   }}
                ]
              } = res
@@ -415,7 +467,13 @@ defmodule AlgoliaxTest.StructTest do
                  {:ok,
                   %Algoliax.Response{
                     response: %{"objectID" => "known"},
-                    params: [index_name: :algoliax_people_struct_fr, object_id: "known"]
+                    params: [
+                      index_name: :algoliax_people_struct_fr,
+                      object_id: "known",
+                      application_id: @application_id
+                    ],
+                    application_id: @application_id,
+                    api_key: @api_key
                   }}
                ]
              } = res2
@@ -487,7 +545,12 @@ defmodule AlgoliaxTest.StructTest do
                  {:ok,
                   %Algoliax.Response{
                     response: %{"searchableAttributes" => ["test"]},
-                    params: [index_name: :algoliax_people_struct_en]
+                    params: [
+                      index_name: :algoliax_people_struct_en,
+                      application_id: @application_id
+                    ],
+                    application_id: @application_id,
+                    api_key: @api_key
                   }}
                ]
              } = res
@@ -498,7 +561,12 @@ defmodule AlgoliaxTest.StructTest do
                  {:ok,
                   %Algoliax.Response{
                     response: %{"searchableAttributes" => ["test"]},
-                    params: [index_name: :algoliax_people_struct_fr]
+                    params: [
+                      index_name: :algoliax_people_struct_fr,
+                      application_id: @application_id
+                    ],
+                    application_id: @application_id,
+                    api_key: @api_key
                   }}
                ]
              } = res2
@@ -551,7 +619,12 @@ defmodule AlgoliaxTest.StructTest do
                  {:ok,
                   %Algoliax.Response{
                     response: %{"taskID" => _, "updatedAt" => _},
-                    params: [index_name: :algoliax_people_struct_en]
+                    params: [
+                      index_name: :algoliax_people_struct_en,
+                      application_id: @application_id
+                    ],
+                    application_id: @application_id,
+                    api_key: @api_key
                   }}
                ]
              } = res
@@ -562,7 +635,12 @@ defmodule AlgoliaxTest.StructTest do
                  {:ok,
                   %Algoliax.Response{
                     response: %{"taskID" => _, "updatedAt" => _},
-                    params: [index_name: :algoliax_people_struct_fr]
+                    params: [
+                      index_name: :algoliax_people_struct_fr,
+                      application_id: @application_id
+                    ],
+                    application_id: @application_id,
+                    api_key: @api_key
                   }}
                ]
              } = res2
@@ -613,7 +691,13 @@ defmodule AlgoliaxTest.StructTest do
                  {:ok,
                   %Algoliax.Response{
                     response: %{"objectID" => "known"},
-                    params: [index_name: :people_runtime_index_name_en, object_id: "known"]
+                    params: [
+                      index_name: :people_runtime_index_name_en,
+                      object_id: "known",
+                      application_id: @application_id
+                    ],
+                    application_id: @application_id,
+                    api_key: @api_key
                   }}
                ]
              } = res
@@ -624,7 +708,13 @@ defmodule AlgoliaxTest.StructTest do
                  {:ok,
                   %Algoliax.Response{
                     response: %{"objectID" => "known"},
-                    params: [index_name: :people_runtime_index_name_fr, object_id: "known"]
+                    params: [
+                      index_name: :people_runtime_index_name_fr,
+                      object_id: "known",
+                      application_id: @application_id
+                    ],
+                    application_id: @application_id,
+                    api_key: @api_key
                   }}
                ]
              } = res2
@@ -638,6 +728,67 @@ defmodule AlgoliaxTest.StructTest do
     end
   end
 
+  describe "configured credentials" do
+    test "get_object/1" do
+      person = %PeopleStructCredentials{
+        reference: "known",
+        last_name: "Doe",
+        first_name: "John",
+        age: 77
+      }
+
+      assert {:ok, res} = PeopleStructCredentials.get_object(person)
+
+      assert %Algoliax.Response{
+               response: %{"objectID" => "known"},
+               params: [
+                 index_name: :people_runtime_index,
+                 object_id: "known",
+                 application_id: "APPLICATION_ID_1"
+               ],
+               application_id: "APPLICATION_ID_1",
+               api_key: "api_key_1"
+             } ==
+               res
+
+      assert_request(
+        "GET",
+        %{
+          path: "/APPLICATION_ID_1/read/people_runtime_index/known",
+          body: %{},
+          headers: [
+            {"x-algolia-api-key", "api_key_1"},
+            {"x-algolia-application-id", "APPLICATION_ID_1"}
+          ]
+        }
+      )
+
+      assert_request(
+        "GET",
+        %{
+          path: "/APPLICATION_ID_1/read/people_runtime_index/settings",
+          body: %{},
+          headers: [
+            {"x-algolia-api-key", "api_key_1"},
+            {"x-algolia-application-id", "APPLICATION_ID_1"}
+          ]
+        }
+      )
+
+      assert_request(
+        "PUT",
+        %{
+          path: "/APPLICATION_ID_1/write/people_runtime_index/settings",
+          body: %{},
+          headers: [
+            {"x-algolia-api-key", "api_key_1"},
+            {"x-algolia-application-id", "APPLICATION_ID_1"}
+          ]
+        }
+      )
+    end
+  end
+
   describe "wait for task" do
     reference = :rand.uniform(1_000_000) |> to_string()
     person = %PeopleStruct{reference: reference, last_name: "Doe", first_name: "John", age: 77}
@@ -669,12 +820,20 @@ defmodule AlgoliaxTest.StructTest do
 
     assert %Algoliax.Response{
              response: %{"objectID" => ^reference, "taskID" => task_id, "updatedAt" => _},
-             params: [index_name: :algoliax_people_struct_en, object_id: ^reference]
+             params: [
+               index_name: :algoliax_people_struct_en,
+               object_id: ^reference,
+               application_id: "APPLICATION_ID"
+             ]
            } = res
 
     assert %Algoliax.Response{
              response: %{"objectID" => ^reference, "taskID" => task_id2, "updatedAt" => _},
-             params: [index_name: :algoliax_people_struct_fr, object_id: ^reference]
+             params: [
+               index_name: :algoliax_people_struct_fr,
+               object_id: ^reference,
+               application_id: "APPLICATION_ID"
+             ]
            } = res2
 
     # Assert that there are 4 calls to check task status per index
diff --git a/test/algoliax/utils_test.exs b/test/algoliax/utils_test.exs
index 134b584..cc4d266 100644
--- a/test/algoliax/utils_test.exs
+++ b/test/algoliax/utils_test.exs
@@ -150,6 +150,42 @@ defmodule Algoliax.UtilsTest do
     end
   end
 
+  describe "api_key/1" do
+    test "with a function" do
+      assert Algoliax.Utils.api_key(credentials: :custom_1) ==
+               "api_key_1"
+    end
+
+    test "without a function (uses Algoliax.Config)" do
+      assert Algoliax.Utils.api_key([]) ==
+               "api_key"
+    end
+
+    test "missing config" do
+      assert_raise(Algoliax.InvalidAlgoliaCredentialsError, fn ->
+        Algoliax.Utils.api_key(credentials: :custom_unknown)
+      end)
+    end
+  end
+
+  describe "application_id/1" do
+    test "with a config" do
+      assert Algoliax.Utils.application_id(credentials: :custom_1) ==
+               "APPLICATION_ID_1"
+    end
+
+    test "without a config (uses Algoliax.Config)" do
+      assert Algoliax.Utils.application_id([]) ==
+               "APPLICATION_ID"
+    end
+
+    test "missing config" do
+      assert_raise(Algoliax.InvalidAlgoliaCredentialsError, fn ->
+        Algoliax.Utils.application_id(credentials: :custom_unknown)
+      end)
+    end
+  end
+
   describe "index_name/2" do
     test "with a function" do
       assert Algoliax.Utils.index_name(IndexNameFromFunction, index_name: :algoliax_people) ==
diff --git a/test/support/schemas/people_struct_runtime_credentials.ex b/test/support/schemas/people_struct_runtime_credentials.ex
new file mode 100644
index 0000000..fd96b5b
--- /dev/null
+++ b/test/support/schemas/people_struct_runtime_credentials.ex
@@ -0,0 +1,15 @@
+defmodule Algoliax.Schemas.PeopleStructCredentials do
+  @moduledoc false
+
+  use Algoliax.Indexer,
+    index_name: :people_runtime_index,
+    object_id: :reference,
+    algolia: [
+      attributes_for_faceting: ["age"],
+      searchable_attributes: ["full_name"],
+      custom_ranking: ["desc(update_at)"]
+    ],
+    credentials: :custom_1
+
+  defstruct reference: nil, last_name: nil, first_name: nil, age: nil
+end