diff --git a/.gitignore b/.gitignore
index c031eb8..8e41f40 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,3 +3,4 @@
 erl_crash.dump
 /doc
 *.ez
+/cover
diff --git a/CHANGELOG.md b/CHANGELOG.md
index c8d8884..f92fa84 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,98 +1,109 @@
 # Changelog
 
+## Unreleased
+
+### Backward Incompatible Changes
+
+- There is no longer a default serializer for `application/json`. Please make
+  sure to register a serializer with `OAuth2.Client.put_serializer/3`.
+- Serializers are now registered via `OAuth2.Client.put_serializer/3`.
+  This change allows applications wrapping `oauth2` a way to provide default
+  serializers without requiring the user to manually configure a serializer.
+
 ## v0.9.4 (2018-10-18)
 
 ### Improvements
 
-* Relaxed `hackney` version requirements
+- Relaxed `hackney` version requirements
 
 ## v0.9.3 (2018-08-13)
 
 ### Bug fixes
 
-* Various type specs fixed
+- Various type specs fixed
 
 ## v0.9.2 (2017-11-17)
 
 ### Bug fixes
 
-* Updates the `OAuth2.Client.get_token!` function to handle error `OAuth2.Response` structs.
+- Updates the `OAuth2.Client.get_token!` function to handle error `OAuth2.Response` structs.
 
 ## v0.9.1 (2017-03-10)
 
 ### Improvements
 
-* Fix dialyzer warnings.
-* Update `hackney` to `1.7`
+- Fix dialyzer warnings.
+- Update `hackney` to `1.7`
 
 ### Bug fixes
 
-* De-dupe headers.
+- De-dupe headers.
 
 ## v0.9.0 (2017-02-02)
 
 ### Improvements
 
-* Remove deprecated usage of `Behaviour` and `defcallback`
-* Provides better support for configuring `request_opts` that will be used on
+- Remove deprecated usage of `Behaviour` and `defcallback`
+- Provides better support for configuring `request_opts` that will be used on
   every request. This is useful for configuring SSL options, etc.
-* Provides support for `hackney`s streaming of responses.
-* Better warnings when a serializer isn't properly configured.
+- Provides support for `hackney`s streaming of responses.
+- Better warnings when a serializer isn't properly configured.
 
 ### Backward Incompatible Changes
 
-* Responses with status codes between `400..599` will now return `{:error,
-  %OAuth2.Response{}}` instead of `{:ok, %OAuth2.Response{}}`
-* When using the `!` versions of functions, `{:error, %OAuth2.Response{}}` will
+- Responses with status codes between `400..599` will now return `{:error, %OAuth2.Response{}}` instead of `{:ok, %OAuth2.Response{}}`
+- When using the `!` versions of functions, `{:error, %OAuth2.Response{}}` will
   be converted to an `%OAuth2.Error{}` and raised.
 
 ## v0.8.3 (2017-01-26)
 
-* Fix compile-time warnings for Elixir 1.4
-* Fix dialyzer warnings on `@type params`
-* Fix `content-type` resolving when there are multiple params
-* Return the same refresh token unless a new one is provided
-* Raise an exception when missing serializer configuration
+- Fix compile-time warnings for Elixir 1.4
+- Fix dialyzer warnings on `@type params`
+- Fix `content-type` resolving when there are multiple params
+- Return the same refresh token unless a new one is provided
+- Raise an exception when missing serializer configuration
 
 ## v0.8.2 (2016-11-22)
 
 ### Bug Fixes
 
-* Fixed an issue in handling non-standard `expires` key in access token
+- Fixed an issue in handling non-standard `expires` key in access token
   requests.
 
 ## v0.8.1 (2016-11-18)
 
 ### Improvements
 
-* Added the ability to debug responses from the provider.
+- Added the ability to debug responses from the provider.
 
 ### Bug Fixes
 
-* Fixed regression in handling `text/plain` content-type for tokens in #74
+- Fixed regression in handling `text/plain` content-type for tokens in #74
 
 ## v0.8.0 (2016-10-05)
 
 ### Improvements
 
-* Added `OAuth2.Client.basic_auth/1` convenience function.
+- Added `OAuth2.Client.basic_auth/1` convenience function.
 
 ### Bug Fixes
 
-* Fixed broken `RefreshToken` strategy reported in #66
-* Fixed an issue where checking the `content-type` was defaulting to
+- Fixed broken `RefreshToken` strategy reported in #66
+- Fixed an issue where checking the `content-type` was defaulting to
   `application/json` causing Poison to explode.
 
 ## v0.7.0 (2016-08-16)
 
 ### Improvements
-* Add support for custom serializers based on MIME types.
-* Remove dependency on `HTTPoison` in favor of using `hackney` directly.
-* Remove dependency on `mimetype_parser`.
-* `Poison` is now only a `test` dependency.
+
+- Add support for custom serializers based on MIME types.
+- Remove dependency on `HTTPoison` in favor of using `hackney` directly.
+- Remove dependency on `mimetype_parser`.
+- `Poison` is now only a `test` dependency.
 
 ### Bug Fixes
-* `expires_in` values that are returned as strings are now properly parsed into integers for `expires_at`.
+
+- `expires_in` values that are returned as strings are now properly parsed into integers for `expires_at`.
 
 ### Backward Incompatible Changes
 
@@ -109,34 +120,36 @@ Please consult the [README](https://github.com/scrogson/oauth2/blob/v0.7.0/READM
 
 The following methods have been moved and adjusted so that they take a `OAuth2.Client.t` which contains a token, rather than a token directly:
 
-* `OAuth2.AccessToken.get` -> `OAuth2.Client.get`
-* `OAuth2.AccessToken.get!` -> `OAuth2.Client.get!`
-* `OAuth2.AccessToken.put` -> `OAuth2.Client.put`
-* `OAuth2.AccessToken.put!` -> `OAuth2.Client.put!`
-* `OAuth2.AccessToken.patch` -> `OAuth2.Client.patch`
-* `OAuth2.AccessToken.patch!` -> `OAuth2.Client.patch!`
-* `OAuth2.AccessToken.post` -> `OAuth2.Client.post`
-* `OAuth2.AccessToken.post!` -> `OAuth2.Client.post!`
-* `OAuth2.AccessToken.delete` -> `OAuth2.Client.delete`
-* `OAuth2.AccessToken.delete!` -> `OAuth2.Client.delete!`
-* `OAuth2.AccessToken.refresh` -> `OAuth2.Client.refresh_token`
-* `OAuth2.AccessToken.refresh!` -> `OAuth2.Client.refresh_token!`
+- `OAuth2.AccessToken.get` -> `OAuth2.Client.get`
+- `OAuth2.AccessToken.get!` -> `OAuth2.Client.get!`
+- `OAuth2.AccessToken.put` -> `OAuth2.Client.put`
+- `OAuth2.AccessToken.put!` -> `OAuth2.Client.put!`
+- `OAuth2.AccessToken.patch` -> `OAuth2.Client.patch`
+- `OAuth2.AccessToken.patch!` -> `OAuth2.Client.patch!`
+- `OAuth2.AccessToken.post` -> `OAuth2.Client.post`
+- `OAuth2.AccessToken.post!` -> `OAuth2.Client.post!`
+- `OAuth2.AccessToken.delete` -> `OAuth2.Client.delete`
+- `OAuth2.AccessToken.delete!` -> `OAuth2.Client.delete!`
+- `OAuth2.AccessToken.refresh` -> `OAuth2.Client.refresh_token`
+- `OAuth2.AccessToken.refresh!` -> `OAuth2.Client.refresh_token!`
 
 Additionally, the following methods have been moved to `OAuth2.Request`
 
-* `OAuth2.AccessToken.request` -> `OAuth2.Request.request`
-* `OAuth2.AccessToken.request!` -> `OAuth2.Request.request!`
+- `OAuth2.AccessToken.request` -> `OAuth2.Request.request`
+- `OAuth2.AccessToken.request!` -> `OAuth2.Request.request!`
 
 Diff: https://github.com/scrogson/oauth2/compare/v0.6.0...v0.7.0
 
 ## v0.6.0 (2016-06-24)
 
 ### Improvements
-* Use Poison ~> 2.0
-* Reset client headers after fetching the token
+
+- Use Poison ~> 2.0
+- Reset client headers after fetching the token
 
 ### Bug Fixes
-* Fix up auth code flow to match the RFC
+
+- Fix up auth code flow to match the RFC
 
 Diff: https://github.com/scrogson/oauth2/compare/v0.5.0...v0.6.0
 
@@ -144,21 +157,21 @@ Diff: https://github.com/scrogson/oauth2/compare/v0.5.0...v0.6.0
 
 ### Improvements
 
-* You can now request a refresh token with `OAuth2.AccessToken.refresh`. The `!` alternative is also available.
-* Added `Bypass` for improved testability.
-* `Plug` is no longer a direct dependency. It is only included as a test dependency through the `Bypass` library.
-* `OAuth2.AccessToken` now supports `DELETE` requests with `delete` and `delete!`
-* More tests!
+- You can now request a refresh token with `OAuth2.AccessToken.refresh`. The `!` alternative is also available.
+- Added `Bypass` for improved testability.
+- `Plug` is no longer a direct dependency. It is only included as a test dependency through the `Bypass` library.
+- `OAuth2.AccessToken` now supports `DELETE` requests with `delete` and `delete!`
+- More tests!
 
 ### Bug Fixes
 
-* Params are no longer sent in both the body and as a query string for `POST` requests with `OAuth2.Client.get_token`
-* Responses will no longer be parsed automatically if the `content-type` is not supported by this lib. Registering custom parsers is a future goal for this library.
-* Errors are now properly raised when they occur.
+- Params are no longer sent in both the body and as a query string for `POST` requests with `OAuth2.Client.get_token`
+- Responses will no longer be parsed automatically if the `content-type` is not supported by this lib. Registering custom parsers is a future goal for this library.
+- Errors are now properly raised when they occur.
 
 ### Backwards Incompatible Changes
 
-* `OAuth2.new/1` has been removed. Use `OAuth2.Client.new/1` instead.
+- `OAuth2.new/1` has been removed. Use `OAuth2.Client.new/1` instead.
 
 Diff: https://github.com/scrogson/oauth2/compare/v0.4.0...v0.5.0
 
@@ -166,17 +179,17 @@ Diff: https://github.com/scrogson/oauth2/compare/v0.4.0...v0.5.0
 
 ### Additions/Improvements
 
-* `OAuth2.AccessToken` now supports: `post`, `post!`, `put`, `put!`, `patch`, and `patch!`.
-* Better documentation
-* Test coverage improved
+- `OAuth2.AccessToken` now supports: `post`, `post!`, `put`, `put!`, `patch`, and `patch!`.
+- Better documentation
+- Test coverage improved
 
 ### Bug fixes
 
-* Empty response bodies are no longer decoded
+- Empty response bodies are no longer decoded
 
 ### Breaking changes
 
-* `OAuth2.AccessToken.get!/4` now returns `OAuth2.Response{}` instead of just the parsed body.
+- `OAuth2.AccessToken.get!/4` now returns `OAuth2.Response{}` instead of just the parsed body.
 
 ### Aknowledgements
 
@@ -190,7 +203,6 @@ Bump `Plug` dependency to `1.0`.
 
 Diff: https://github.com/scrogson/oauth2/compare/v0.2.0...v0.3.0
 
-
 ## v0.2.0 (2015-07-13)
 
 - `:erlang.now` was replaced with `:os.timestamp` for compatibility with Erlang 18
@@ -198,7 +210,6 @@ Diff: https://github.com/scrogson/oauth2/compare/v0.2.0...v0.3.0
 
 Diff: https://github.com/scrogson/oauth2/compare/v0.1.1...v0.2.0
 
-
 ## v0.1.1 (2015-04-18)
 
 - Remove compilation warnings.
@@ -206,7 +217,6 @@ Diff: https://github.com/scrogson/oauth2/compare/v0.1.1...v0.2.0
 
 Diff: https://github.com/scrogson/oauth2/compare/v0.1.0...v0.1.1
 
-
 ## v0.1.0 (2015-04-14)
 
 This release bring breaking changes and more documentation.
@@ -215,7 +225,6 @@ Please see the [README](https://github.com/scrogson/oauth2/blob/v0.1.0/README.md
 
 Diff: https://github.com/scrogson/oauth2/compare/v0.0.5...v0.1.0
 
-
 ## v0.0.5 (2015-04-11)
 
 - Handles Facebooks `expires` key for Access Tokens.
@@ -223,7 +232,6 @@ Diff: https://github.com/scrogson/oauth2/compare/v0.0.5...v0.1.0
 
 Diff: https://github.com/scrogson/oauth2/compare/0.0.3...v0.0.5
 
-
 ## v0.0.3 (2015-01-12)
 
 - Relax version requirements for Poison.
@@ -240,4 +248,3 @@ http://tools.ietf.org/html/draft-ietf-oauth-v2-15#section-4.4
 Initial release.
 
 This initial release includes a functional authorization code strategy: http://tools.ietf.org/html/draft-ietf-oauth-v2-15#section-4.1
-
diff --git a/README.md b/README.md
index 8799623..9ceb91c 100644
--- a/README.md
+++ b/README.md
@@ -25,35 +25,27 @@ end
 ## Configure a serializer
 
 This library can be configured to handle encoding and decoding requests and
-responses automatically.
+responses automatically based on the `accept` and/or `content-type` headers.
 
-If you're using [Poison](https://hex.pm/packages/poison) for JSON in your
-application, this library is already pre-configured to use it for `"application/json"`
-request and response bodies. You will still need to include it as a dependency though.
-
-If you need to handle different MIME types, you can simply configure it like so:
+If you need to handle various MIME types, you can simply register serializers like so:
 
 ```elixir
-# config/config.exs
-config :oauth2,
-  serializers: %{
-    "application/vnd.api+json" => Poison,
-    "application/xml" => MyApp.XmlParser,
-  }
+OAuth2.Client.put_serializer(client, "application/vnd.api+json", Jason)
+OAuth2.Client.put_serializer(client, "application/xml", MyApp.Parsers.XML)
 ```
 
-The `serializers` option is a map where the keys are MIME types and the values
-are modules.
-
 The modules are expected to export `encode!/1` and `decode!/1`.
 
 ```elixir
-defmodule MyApp.XmlParser do
+defmodule MyApp.Parsers.XML do
   def encode!(data), do: # ...
   def decode!(binary), do: # ...
 end
 ```
 
+Please see the documentation for [OAuth2.Serializer](https://hexdocs.pm/oauth2/OAuth2.Serializer.html)
+for more details.
+
 ## Debug mode
 
 Some times its handy to see what's coming back from the response when getting
@@ -158,6 +150,7 @@ defmodule GitHub do
       authorize_url: "https://github.com/login/oauth/authorize",
       token_url: "https://github.com/login/oauth/access_token"
     ])
+    |> OAuth2.Client.put_serializer("application/json", Jason)
   end
 
   def authorize_url! do
diff --git a/config/config.exs b/config/config.exs
index 473fc5c..a2d3221 100644
--- a/config/config.exs
+++ b/config/config.exs
@@ -1,10 +1,9 @@
 use Mix.Config
 
-config :logger, level: :info
+config :logger, level: :debug
 
 config :oauth2,
   client_id: "0bee1126b1a1381d9cab60bcd52349484451808a", # first commit sha of this library
   client_secret: "f715d64092fe81c396ac383e97f8a7eca40e7c89", #second commit sha
   redirect_uri: "http://example.com/auth/callback",
-  serializers: %{"application/json" => Poison},
   request_opts: []
diff --git a/coveralls.json b/coveralls.json
new file mode 100644
index 0000000..20ac360
--- /dev/null
+++ b/coveralls.json
@@ -0,0 +1,6 @@
+{
+  "skip_files": [
+    "lib/oauth2/strategy.ex",
+    "test/support/test_helpers.ex"
+  ]
+}
diff --git a/lib/oauth2/client.ex b/lib/oauth2/client.ex
index b234049..87e2ba5 100644
--- a/lib/oauth2/client.ex
+++ b/lib/oauth2/client.ex
@@ -41,6 +41,7 @@ defmodule OAuth2.Client do
   @type redirect_uri  :: binary
   @type ref           :: reference | nil
   @type request_opts  :: Keyword.t
+  @type serializers   :: %{binary => module}
   @type site          :: binary
   @type strategy      :: module
   @type token         :: AccessToken.t | nil
@@ -56,6 +57,7 @@ defmodule OAuth2.Client do
     redirect_uri:  redirect_uri,
     ref:           ref,
     request_opts:  request_opts,
+    serializers:   serializers,
     site:          site,
     strategy:      strategy,
     token:         token,
@@ -71,6 +73,7 @@ defmodule OAuth2.Client do
             redirect_uri: "",
             ref: nil,
             request_opts: [],
+            serializers: %{},
             site: "",
             strategy: OAuth2.Strategy.AuthCode,
             token: nil,
@@ -179,7 +182,9 @@ defmodule OAuth2.Client do
   @spec put_headers(t, list) :: t
   def put_headers(%Client{} = client, []), do: client
   def put_headers(%Client{} = client, [{k,v}|rest]) do
-    client |> put_header(k,v) |> put_headers(rest)
+    client
+    |> put_header(k, v)
+    |> put_headers(rest)
   end
 
   @doc false
@@ -202,6 +207,43 @@ defmodule OAuth2.Client do
     url
   end
 
+  @doc """
+  Register a serialization module for a given mime type.
+
+  ## Example
+
+      iex> client = OAuth2.Client.put_serializer(%OAuth2.Client{}, "application/json", Jason)
+      %OAuth2.Client{serializers: %{"application/json" => Jason}}
+      iex> OAuth2.Client.get_serializer(client, "application/json")
+      Jason
+  """
+  @spec put_serializer(t, binary, atom) :: t
+  def put_serializer(%Client{serializers: serializers} = client, mime, module)
+    when is_binary(mime) and is_atom(module) do
+    %Client{client | serializers: Map.put(serializers, mime, module)}
+  end
+
+  @doc """
+  Un-register a serialization module for a given mime type.
+
+  ## Example
+
+      iex> client = OAuth2.Client.delete_serializer(%OAuth2.Client{}, "application/json")
+      %OAuth2.Client{}
+      iex> OAuth2.Client.get_serializer(client, "application/json")
+      nil
+  """
+  @spec delete_serializer(t, binary) :: t
+  def delete_serializer(%Client{serializers: serializers} = client, mime) do
+    %Client{client | serializers: Map.delete(serializers, mime)}
+  end
+
+  @doc false
+  @spec get_serializer(t, binary) :: atom
+  def get_serializer(%Client{serializers: serializers}, mime) do
+    Map.get(serializers, mime)
+  end
+
   @doc """
   Fetches an `OAuth2.AccessToken` struct by making a request to the token endpoint.
 
diff --git a/lib/oauth2/request.ex b/lib/oauth2/request.ex
index 9933bea..0dfb40c 100644
--- a/lib/oauth2/request.ex
+++ b/lib/oauth2/request.ex
@@ -1,10 +1,10 @@
 defmodule OAuth2.Request do
   @moduledoc false
-  
+
   require Logger
   import OAuth2.Util
 
-  alias OAuth2.{Client, Error, Response, Serializer}
+  alias OAuth2.{Client, Error, Response}
 
   @type body :: any
 
@@ -17,13 +17,14 @@ defmodule OAuth2.Request do
     url = client |> process_url(url) |> process_params(opts[:params])
     headers = req_headers(client, headers) |> Enum.uniq
     content_type = content_type(headers)
-    body = encode_request_body(body, content_type)
+    serializer = Client.get_serializer(client, content_type)
+    body = encode_request_body(body, content_type, serializer)
     headers = process_request_headers(headers, content_type)
     req_opts = Keyword.merge(client.request_opts, opts)
 
     if Application.get_env(:oauth2, :debug) do
       Logger.debug("""
-        OAuth2 Provider Request 
+        OAuth2 Provider Request
         url: #{inspect url}
         method: #{inspect method}
         headers: #{inspect headers}
@@ -36,9 +37,9 @@ defmodule OAuth2.Request do
       {:ok, ref} when is_reference(ref) ->
         {:ok, ref}
       {:ok, status, headers, ref} when is_reference(ref) ->
-        process_body(status, headers, ref)
+        process_body(client, status, headers, ref)
       {:ok, status, headers, body} when is_binary(body) ->
-        process_body(status, headers, body)
+        process_body(client, status, headers, body)
       {:error, reason} ->
         {:error, %Error{reason: reason}}
     end
@@ -80,16 +81,16 @@ defmodule OAuth2.Request do
     end
   end
 
-  defp process_body(status, headers, ref) when is_reference(ref) do
+  defp process_body(client, status, headers, ref) when is_reference(ref) do
     case :hackney.body(ref) do
       {:ok, body} ->
-        process_body(status, headers, body)
+        process_body(client, status, headers, body)
       {:error, reason} ->
         {:error, %Error{reason: reason}}
     end
   end
-  defp process_body(status, headers, body) when is_binary(body) do
-    resp = Response.new(status, headers, body)
+  defp process_body(client, status, headers, body) when is_binary(body) do
+    resp = Response.new(client, status, headers, body)
     case status do
       status when status in 200..399 ->
         {:ok, resp}
@@ -120,9 +121,14 @@ defmodule OAuth2.Request do
     end
   end
 
-  defp encode_request_body("", _), do: ""
-  defp encode_request_body([], _), do: ""
-  defp encode_request_body(body, "application/x-www-form-urlencoded"),
+  defp encode_request_body("", _, _), do: ""
+  defp encode_request_body([], _, _), do: ""
+  defp encode_request_body(body, "application/x-www-form-urlencoded", _),
     do: URI.encode_query(body)
-  defp encode_request_body(body, type), do: Serializer.encode!(body, type)
+  defp encode_request_body(body, _mime, nil) do
+    body
+  end
+  defp encode_request_body(body, _mime, serializer) do
+    serializer.encode!(body)
+  end
 end
diff --git a/lib/oauth2/response.ex b/lib/oauth2/response.ex
index 0353338..0b6e958 100644
--- a/lib/oauth2/response.ex
+++ b/lib/oauth2/response.ex
@@ -12,7 +12,7 @@ defmodule OAuth2.Response do
 
   require Logger
   import OAuth2.Util
-  alias OAuth2.Serializer
+  alias OAuth2.Client
 
   @type status_code :: integer
   @type headers     :: list
@@ -27,9 +27,11 @@ defmodule OAuth2.Response do
   defstruct status_code: nil, headers: [], body: nil
 
   @doc false
-  def new(code, headers, body) do
+  def new(client, code, headers, body) do
     headers = process_headers(headers)
-    body = decode_response_body(body, content_type(headers))
+    content_type = content_type(headers)
+    serializer = Client.get_serializer(client, content_type)
+    body = decode_response_body(body, content_type, serializer)
     resp = %__MODULE__{status_code: code, headers: headers, body: body}
 
     if Application.get_env(:oauth2, :debug) do
@@ -43,16 +45,22 @@ defmodule OAuth2.Response do
     Enum.map(headers, fn {k, v} -> {String.downcase(k), v} end)
   end
 
-  defp decode_response_body("", _type), do: ""
-  defp decode_response_body(" ", _type), do: ""
+  defp decode_response_body("", _type, _), do: ""
+  defp decode_response_body(" ", _type, _), do: ""
   # Facebook sends text/plain tokens!?
-  defp decode_response_body(body, "text/plain") do
+  defp decode_response_body(body, "text/plain", _) do
     case URI.decode_query(body) do
       %{"access_token" => _} = token -> token
       _ -> body
     end
   end
-  defp decode_response_body(body, "application/x-www-form-urlencoded"),
-    do: URI.decode_query(body)
-  defp decode_response_body(body, type), do: Serializer.decode!(body, type)
+  defp decode_response_body(body, "application/x-www-form-urlencoded", _) do
+    URI.decode_query(body)
+  end
+  defp decode_response_body(body, _mime, nil) do
+    body
+  end
+  defp decode_response_body(body, _type, serializer) do
+    serializer.decode!(body)
+  end
 end
diff --git a/lib/oauth2/serializer.ex b/lib/oauth2/serializer.ex
index 826cb7e..7fffcd8 100644
--- a/lib/oauth2/serializer.ex
+++ b/lib/oauth2/serializer.ex
@@ -1,50 +1,15 @@
 defmodule OAuth2.Serializer do
-  @moduledoc false
+  @moduledoc """
+  A serializer is responsible for encoding/decoding request/response bodies.
 
-  require Logger
+  ## Example
 
-  defmodule NullSerializer do
-    @moduledoc false
+      defmodule MyApp.JSON do
+        def encode!(data), do: Jason.encode!(data)
+        def decode!(binary), do: Jason.decode!(binary)
+      end
+  """
 
-    @doc false
-    def decode!(content), do: content
-
-    @doc false
-    def encode!(content), do: content
-  end
-
-  def decode!(content, type), do: serializer(type).decode!(content)
-
-  def encode!(content, type), do: serializer(type).encode!(content)
-
-  defp serializer(type) do
-    serializer = Map.get(configured_serializers(), type, NullSerializer)
-    warn_missing_serializer = Application.get_env(:oauth2, :warn_missing_serializer, true)
-
-    if serializer == NullSerializer && warn_missing_serializer do
-      Logger.warn """
-
-      A serializer was not configured for content-type '#{type}'.
-
-      To remove this warning for this content-type, add the following to your `config.exs` file:
-
-          config :oauth2,
-            serializers: %{
-              "#{type}" => MySerializer
-            }
-
-      To remove this warning entirely, add the following to you `config.exs` file:
-
-          config :oauth2,
-            warn_missing_serializer: false
-      """
-    end
-
-    serializer
-  end
-
-  defp configured_serializers do
-    Application.get_env(:oauth2, :serializers) ||
-      raise("Missing serializers configuration! Make sure oauth2 app is added to mix application list")
-  end
+  @callback encode!(map) :: binary
+  @callback decode!(binary) :: map
 end
diff --git a/mix.exs b/mix.exs
index dcbc179..74935cd 100644
--- a/mix.exs
+++ b/mix.exs
@@ -22,17 +22,17 @@ defmodule OAuth2.Mixfile do
   end
 
   def application do
-    [applications: [:logger, :hackney],
-     env: [serializers: %{"application/json" => Poison}]]
+    [applications: [:logger, :hackney]]
   end
 
   defp deps do
-    [{:hackney, "~> 1.7"},
+    [{:hackney, "~> 1.13.0"},
 
      # Test dependencies
-     {:poison, "~> 3.0", only: :test},
-     {:bypass, "~> 0.6", only: :test},
-     {:excoveralls, "~> 0.5", only: :test},
+     {:jason, "~> 1.0", only: :test},
+     {:bypass, "~> 0.9", only: :test},
+     {:plug_cowboy, "~> 1.0", only: :test},
+     {:excoveralls, "~> 0.9", only: :test},
      {:dialyxir, "~> 0.5", only: [:dev], runtime: false},
 
      # Docs dependencies
diff --git a/mix.lock b/mix.lock
index 770be31..61fa37a 100644
--- a/mix.lock
+++ b/mix.lock
@@ -1,24 +1,26 @@
 %{
-  "bypass": {:hex, :bypass, "0.6.0", "fd0a8004fada4464e2ba98497755310b892a097f2fd975f4f787cf264066a335", [:mix], [{:cowboy, "~> 1.0", [repo: "hexpm", hex: :cowboy, optional: false]}, {:plug, "~> 1.0", [repo: "hexpm", hex: :plug, optional: false]}], "hexpm"},
-  "certifi": {:hex, :certifi, "1.0.0", "1c787a85b1855ba354f0b8920392c19aa1d06b0ee1362f9141279620a5be2039", [:rebar3], [], "hexpm"},
-  "cowboy": {:hex, :cowboy, "1.1.2", "61ac29ea970389a88eca5a65601460162d370a70018afe6f949a29dca91f3bb0", [:rebar3], [{:cowlib, "~> 1.0.2", [hex: :cowlib, optional: false]}, {:ranch, "~> 1.3.2", [hex: :ranch, optional: false]}]},
-  "cowlib": {:hex, :cowlib, "1.0.2", "9d769a1d062c9c3ac753096f868ca121e2730b9a377de23dec0f7e08b1df84ee", [:make], []},
-  "dialyxir": {:hex, :dialyxir, "0.5.0", "5bc543f9c28ecd51b99cc1a685a3c2a1a93216990347f259406a910cf048d1d7", [:mix], []},
+  "bypass": {:hex, :bypass, "0.9.0", "4cedcd326eeec497e0090a73d351cbd0f11e39329ddf9095931b03da9b6dc417", [:mix], [{:cowboy, "~> 1.0 or ~> 2.0", [hex: :cowboy, repo: "hexpm", optional: false]}, {:plug, "~> 1.0", [hex: :plug, repo: "hexpm", optional: false]}], "hexpm"},
+  "certifi": {:hex, :certifi, "2.3.1", "d0f424232390bf47d82da8478022301c561cf6445b5b5fb6a84d49a9e76d2639", [:rebar3], [{:parse_trans, "3.2.0", [hex: :parse_trans, repo: "hexpm", optional: false]}], "hexpm"},
+  "cowboy": {:hex, :cowboy, "1.1.2", "61ac29ea970389a88eca5a65601460162d370a70018afe6f949a29dca91f3bb0", [:rebar3], [{:cowlib, "~> 1.0.2", [hex: :cowlib, repo: "hexpm", optional: false]}, {:ranch, "~> 1.3.2", [hex: :ranch, repo: "hexpm", optional: false]}], "hexpm"},
+  "cowlib": {:hex, :cowlib, "1.0.2", "9d769a1d062c9c3ac753096f868ca121e2730b9a377de23dec0f7e08b1df84ee", [:make], [], "hexpm"},
+  "dialyxir": {:hex, :dialyxir, "0.5.1", "b331b091720fd93e878137add264bac4f644e1ddae07a70bf7062c7862c4b952", [:mix], [], "hexpm"},
   "earmark": {:hex, :earmark, "1.2.6", "b6da42b3831458d3ecc57314dff3051b080b9b2be88c2e5aa41cd642a5b044ed", [:mix], [], "hexpm"},
   "ex_doc": {:hex, :ex_doc, "0.19.1", "519bb9c19526ca51d326c060cb1778d4a9056b190086a8c6c115828eaccea6cf", [:mix], [{:earmark, "~> 1.1", [hex: :earmark, repo: "hexpm", optional: false]}, {:makeup_elixir, "~> 0.7", [hex: :makeup_elixir, repo: "hexpm", optional: false]}], "hexpm"},
-  "excoveralls": {:hex, :excoveralls, "0.6.1", "9e946b6db84dba592f47632157ecd135a46384b98a430fd16007dc910c70348b", [:mix], [{:exjsx, "~> 3.0", [repo: "hexpm", hex: :exjsx, optional: false]}, {:hackney, ">= 0.12.0", [repo: "hexpm", hex: :hackney, optional: false]}], "hexpm"},
-  "exjsx": {:hex, :exjsx, "3.2.1", "1bc5bf1e4fd249104178f0885030bcd75a4526f4d2a1e976f4b428d347614f0f", [:mix], [{:jsx, "~> 2.8.0", [hex: :jsx, optional: false]}]},
-  "hackney": {:hex, :hackney, "1.7.1", "e238c52c5df3c3b16ce613d3a51c7220a784d734879b1e231c9babd433ac1cb4", [:rebar3], [{:certifi, "1.0.0", [repo: "hexpm", hex: :certifi, optional: false]}, {:idna, "4.0.0", [repo: "hexpm", hex: :idna, optional: false]}, {:metrics, "1.0.1", [repo: "hexpm", hex: :metrics, optional: false]}, {:mimerl, "1.0.2", [repo: "hexpm", hex: :mimerl, optional: false]}, {:ssl_verify_fun, "1.1.1", [repo: "hexpm", hex: :ssl_verify_fun, optional: false]}], "hexpm"},
-  "idna": {:hex, :idna, "4.0.0", "10aaa9f79d0b12cf0def53038547855b91144f1bfcc0ec73494f38bb7b9c4961", [:rebar3], [], "hexpm"},
-  "jsx": {:hex, :jsx, "2.8.1", "1453b4eb3615acb3e2cd0a105d27e6761e2ed2e501ac0b390f5bbec497669846", [:mix, :rebar3], []},
+  "excoveralls": {:hex, :excoveralls, "0.10.1", "407d50ac8fc63dfee9175ccb4548e6c5512b5052afa63eedb9cd452a32a91495", [:mix], [{:hackney, "~> 1.13", [hex: :hackney, repo: "hexpm", optional: false]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: false]}], "hexpm"},
+  "hackney": {:hex, :hackney, "1.13.0", "24edc8cd2b28e1c652593833862435c80661834f6c9344e84b6a2255e7aeef03", [:rebar3], [{:certifi, "2.3.1", [hex: :certifi, repo: "hexpm", optional: false]}, {:idna, "5.1.2", [hex: :idna, repo: "hexpm", optional: false]}, {:metrics, "1.0.1", [hex: :metrics, repo: "hexpm", optional: false]}, {:mimerl, "1.0.2", [hex: :mimerl, repo: "hexpm", optional: false]}, {:ssl_verify_fun, "1.1.1", [hex: :ssl_verify_fun, repo: "hexpm", optional: false]}], "hexpm"},
+  "idna": {:hex, :idna, "5.1.2", "e21cb58a09f0228a9e0b95eaa1217f1bcfc31a1aaa6e1fdf2f53a33f7dbd9494", [:rebar3], [{:unicode_util_compat, "0.3.1", [hex: :unicode_util_compat, repo: "hexpm", optional: false]}], "hexpm"},
+  "jason": {:hex, :jason, "1.1.2", "b03dedea67a99223a2eaf9f1264ce37154564de899fd3d8b9a21b1a6fd64afe7", [:mix], [{:decimal, "~> 1.0", [hex: :decimal, repo: "hexpm", optional: true]}], "hexpm"},
   "makeup": {:hex, :makeup, "0.5.5", "9e08dfc45280c5684d771ad58159f718a7b5788596099bdfb0284597d368a882", [:mix], [{:nimble_parsec, "~> 0.4", [hex: :nimble_parsec, repo: "hexpm", optional: false]}], "hexpm"},
   "makeup_elixir": {:hex, :makeup_elixir, "0.10.0", "0f09c2ddf352887a956d84f8f7e702111122ca32fbbc84c2f0569b8b65cbf7fa", [:mix], [{:makeup, "~> 0.5.5", [hex: :makeup, repo: "hexpm", optional: false]}], "hexpm"},
-  "metrics": {:hex, :metrics, "1.0.1", "25f094dea2cda98213cecc3aeff09e940299d950904393b2a29d191c346a8486", [:rebar3], []},
-  "mime": {:hex, :mime, "1.1.0", "01c1d6f4083d8aa5c7b8c246ade95139620ef8effb009edde934e0ec3b28090a", [:mix], [], "hexpm"},
-  "mimerl": {:hex, :mimerl, "1.0.2", "993f9b0e084083405ed8252b99460c4f0563e41729ab42d9074fd5e52439be88", [:rebar3], []},
+  "metrics": {:hex, :metrics, "1.0.1", "25f094dea2cda98213cecc3aeff09e940299d950904393b2a29d191c346a8486", [:rebar3], [], "hexpm"},
+  "mime": {:hex, :mime, "1.3.0", "5e8d45a39e95c650900d03f897fbf99ae04f60ab1daa4a34c7a20a5151b7a5fe", [:mix], [], "hexpm"},
+  "mimerl": {:hex, :mimerl, "1.0.2", "993f9b0e084083405ed8252b99460c4f0563e41729ab42d9074fd5e52439be88", [:rebar3], [], "hexpm"},
   "nimble_parsec": {:hex, :nimble_parsec, "0.4.0", "ee261bb53214943679422be70f1658fff573c5d0b0a1ecd0f18738944f818efe", [:mix], [], "hexpm"},
-  "plug": {:hex, :plug, "1.3.3", "d9be189924379b4e9d470caef87380d09549aea1ceafe6a0d41292c8c317c923", [:mix], [{:cowboy, "~> 1.0.1 or ~> 1.1", [repo: "hexpm", hex: :cowboy, optional: true]}, {:mime, "~> 1.0", [repo: "hexpm", hex: :mime, optional: false]}], "hexpm"},
-  "poison": {:hex, :poison, "3.1.0", "d9eb636610e096f86f25d9a46f35a9facac35609a7591b3be3326e99a0484665", [:mix], []},
-  "ranch": {:hex, :ranch, "1.3.2", "e4965a144dc9fbe70e5c077c65e73c57165416a901bd02ea899cfd95aa890986", [:rebar3], []},
-  "ssl_verify_fun": {:hex, :ssl_verify_fun, "1.1.1", "28a4d65b7f59893bc2c7de786dec1e1555bd742d336043fe644ae956c3497fbe", [:make, :rebar], []},
+  "parse_trans": {:hex, :parse_trans, "3.2.0", "2adfa4daf80c14dc36f522cf190eb5c4ee3e28008fc6394397c16f62a26258c2", [:rebar3], [], "hexpm"},
+  "plug": {:hex, :plug, "1.7.0", "cd8c8de89bd9de55eba1c918bf0e7f319737e109b6014875104af025a623e16e", [:mix], [{:mime, "~> 1.0", [hex: :mime, repo: "hexpm", optional: false]}, {:plug_crypto, "~> 1.0", [hex: :plug_crypto, repo: "hexpm", optional: false]}], "hexpm"},
+  "plug_cowboy": {:hex, :plug_cowboy, "1.0.0", "2e2a7d3409746d335f451218b8bb0858301c3de6d668c3052716c909936eb57a", [:mix], [{:cowboy, "~> 1.0", [hex: :cowboy, repo: "hexpm", optional: false]}, {:plug, "~> 1.7", [hex: :plug, repo: "hexpm", optional: false]}], "hexpm"},
+  "plug_crypto": {:hex, :plug_crypto, "1.0.0", "18e49317d3fa343f24620ed22795ec29d4a5e602d52d1513ccea0b07d8ea7d4d", [:mix], [], "hexpm"},
+  "ranch": {:hex, :ranch, "1.3.2", "e4965a144dc9fbe70e5c077c65e73c57165416a901bd02ea899cfd95aa890986", [:rebar3], [], "hexpm"},
+  "ssl_verify_fun": {:hex, :ssl_verify_fun, "1.1.1", "28a4d65b7f59893bc2c7de786dec1e1555bd742d336043fe644ae956c3497fbe", [:make, :rebar], [], "hexpm"},
+  "unicode_util_compat": {:hex, :unicode_util_compat, "0.3.1", "a1f612a7b512638634a603c8f401892afbf99b8ce93a45041f8aaca99cadb85e", [:rebar3], [], "hexpm"},
 }
diff --git a/test/oauth2/access_token_test.exs b/test/oauth2/access_token_test.exs
index 2dcd82b..b786ba0 100644
--- a/test/oauth2/access_token_test.exs
+++ b/test/oauth2/access_token_test.exs
@@ -4,7 +4,7 @@ defmodule OAuth2.AccessTokenTest do
 
   import OAuth2.TestHelpers, only: [unix_now: 0]
 
-  alias OAuth2.{AccessToken, Response}
+  alias OAuth2.{AccessToken, Client, Response}
 
   test "new from binary token" do
     token = AccessToken.new("abc123")
@@ -12,7 +12,7 @@ defmodule OAuth2.AccessTokenTest do
   end
 
   test "new with 'expires_in' param" do
-    response = Response.new(200, [{"content-type", "application/x-www-form-urlencoded"}], "access_token=abc123&expires_in=123")
+    response = Response.new(%Client{}, 200, [{"content-type", "application/x-www-form-urlencoded"}], "access_token=abc123&expires_in=123")
     token = AccessToken.new(response.body)
     assert token.access_token == "abc123"
     assert token.expires_at == 123 + unix_now()
@@ -21,7 +21,7 @@ defmodule OAuth2.AccessTokenTest do
   end
 
   test "new with 'expires' param" do
-    response = Response.new(200, [{"content-type", "application/x-www-form-urlencoded"}], "access_token=abc123&expires=123")
+    response = Response.new(%Client{}, 200, [{"content-type", "application/x-www-form-urlencoded"}], "access_token=abc123&expires=123")
     token = AccessToken.new(response.body)
     assert token.access_token == "abc123"
     assert token.expires_at == 123 + unix_now()
@@ -30,7 +30,7 @@ defmodule OAuth2.AccessTokenTest do
   end
 
   test "new from text/plain content-type" do
-    response = Response.new(200, [{"content-type", "text/plain"}], "access_token=abc123&expires=123")
+    response = Response.new(%Client{}, 200, [{"content-type", "text/plain"}], "access_token=abc123&expires=123")
     token = AccessToken.new(response.body)
     assert token.access_token == "abc123"
     assert token.expires_at == 123 + unix_now()
diff --git a/test/oauth2/error_test.exs b/test/oauth2/error_test.exs
new file mode 100644
index 0000000..063a3a7
--- /dev/null
+++ b/test/oauth2/error_test.exs
@@ -0,0 +1,11 @@
+defmodule OAuth2.ErrorTest do
+  use ExUnit.Case, async: false
+
+  alias OAuth2.Error
+
+  test "message" do
+    assert Error.message(%Error{reason: :econnrefused}) == "Connection refused"
+    assert Error.message(%Error{reason: "blah"}) == "blah"
+    assert Error.message(%Error{reason: :blah}) == ":blah"
+  end
+end
diff --git a/test/oauth2/response_test.exs b/test/oauth2/response_test.exs
new file mode 100644
index 0000000..2fae594
--- /dev/null
+++ b/test/oauth2/response_test.exs
@@ -0,0 +1,22 @@
+defmodule OAuth2.ResponseTest do
+  use ExUnit.Case, async: false
+
+  alias OAuth2.Response
+
+  import ExUnit.CaptureLog
+
+  test "debug response body" do
+    Application.put_env(:oauth2, :debug, true)
+
+    output = capture_log(fn -> Response.new(%OAuth2.Client{}, 200, [{"content-type", "text/plain"}], "hello") end)
+    assert output =~ ~s(OAuth2 Provider Response)
+    assert output =~ ~s(body: "hello")
+
+    Application.put_env(:oauth2, :debug, false)
+  end
+
+  test "text/plain body passes through body" do
+    response = Response.new(%OAuth2.Client{}, 200, [{"content-type", "text/plain"}], "hello")
+    assert response.body == "hello"
+  end
+end
diff --git a/test/oauth2_test.exs b/test/oauth2_test.exs
index 64a3938..99f1188 100644
--- a/test/oauth2_test.exs
+++ b/test/oauth2_test.exs
@@ -2,6 +2,8 @@ defmodule OAuth2Test do
   use ExUnit.Case
   import OAuth2.TestHelpers
 
+  doctest OAuth2
+
   @client build_client(client_id: "abc123",
                      client_secret: "xyz987",
                      site: "https://api.github.com",
diff --git a/test/serializer_test.exs b/test/serializer_test.exs
deleted file mode 100644
index 9462258..0000000
--- a/test/serializer_test.exs
+++ /dev/null
@@ -1,44 +0,0 @@
-defmodule OAuth2.SerializerTest do
-  use ExUnit.Case
-  alias OAuth2.Serializer
-
-  defmodule TestSerializer do
-    def decode!(_), do: "decode_ok"
-    def encode!(_), do: "encode_ok"
-  end
-  @json_mime "application/json"
-
-  def with_serializers(serializers, fun) do
-    backup = Application.get_env(:oauth2, :serializers)
-    try do
-      Application.put_env(:oauth2, :serializers, serializers)
-      fun.()
-    after
-      Application.put_env(:oauth2, :serializers, backup)
-    end
-  end
-
-  test "has default json serializer" do
-    decoded = Serializer.decode!("{\"foo\": 1}", @json_mime)
-    assert decoded == %{"foo" => 1}
-  end
-
-  test "accepts serializer override" do
-    with_serializers(%{@json_mime => TestSerializer}, fn ->
-      decoded = Serializer.decode!("{\"foo\": 1}", @json_mime)
-      assert decoded == "decode_ok"
-
-      encoded = Serializer.encode!(%{"foo" => 1}, @json_mime)
-      assert encoded == "encode_ok"
-    end)
-  end
-
-  test "raise error when serializers are misconfigured" do
-    with_serializers(nil, fn ->
-      assert_raise(RuntimeError, ~r/configuration/i, fn ->
-        Serializer.decode!("{\"foo\": 1}", @json_mime)
-      end)
-    end)
-  end
-end
-
diff --git a/test/support/test_helpers.ex b/test/support/test_helpers.ex
index 4dd71e6..4a04798 100644
--- a/test/support/test_helpers.ex
+++ b/test/support/test_helpers.ex
@@ -34,7 +34,7 @@ defmodule OAuth2.TestHelpers do
   defp parse_req_body(conn) do
     opts = [parsers: [:urlencoded, :json],
             pass: ["*/*"],
-            json_decoder: Poison]
+            json_decoder: Jason]
     Plug.Parsers.call(conn, Plug.Parsers.init(opts))
   end
 
@@ -55,13 +55,14 @@ defmodule OAuth2.TestHelpers do
   def json(conn, status, body \\ []) do
     conn
     |> put_resp_header("content-type", "application/json")
-    |> send_resp(status, Poison.encode!(body))
+    |> send_resp(status, Jason.encode!(body))
   end
 
   def build_client(opts \\ []) do
     default_client_opts()
     |> Keyword.merge(opts)
     |> OAuth2.Client.new()
+    |> OAuth2.Client.put_serializer("application/json", Jason)
   end
 
   def tokenize_client(opts \\ [], %OAuth2.Client{} = client) do
diff --git a/test/test_helper.exs b/test/test_helper.exs
index 8c2aa6f..98fd96f 100644
--- a/test/test_helper.exs
+++ b/test/test_helper.exs
@@ -1,2 +1,3 @@
 Application.ensure_all_started(:bypass)
-ExUnit.start
+Application.put_env(:oauth2, :warn_missing_serializer, false)
+ExUnit.start()