Update OAuth2.Client.get_token! errors (#98)

* Update OAuth2.Client.get_token! errors

Updates the `OAuth2.Client.get_token!` function to handle error OAuth2.Response structs. I sent some incomplete data to Facebook Graph and saw this error bubble up:

```
[error] %ArgumentError{message: "raise/1 expects a module name, string or exception as the first argument, got: %OAuth2.Response{body: %{\"error\" => %{\"code\" => 101, \"fbtrace_id\" => \"Eelth+pfiU9\", \"message\" => \"Missing client_id parameter.\", \"type\" => \"OAuthException\"}}, headers: [{\"www-authenticate\", \"OAuth \\\"Facebook Platform\\\" \\\"invalid_client\\\" \\\"Missing client_id parameter.\\\"\"}, {\"access-control-allow-origin\", \"*\"}, {\"pragma\", \"no-cache\"}, {\"cache-control\", \"no-store\"}, {\"x-fb-rev\", \"3349395\"}, {\"content-type\", \"application/json\"}, {\"x-fb-trace-id\", \"Eelth+pfiU9\"}, {\"facebook-api-version\", \"v2.8\"}, {\"expires\", \"Sat, 01 Jan 2000 00:00:00 GMT\"}, {\"x-fb-debug\", \"9GWPCrYAIzlrSnt0iLqP/3E4hdmOJpP7QXxBOXTG2Ew7CloqVwka+HXAjyCTewfTaH0F/sUVkDLMcm7+6jOEEQ==\"}, {\"date\", \"Thu, 05 Oct 2017 15:36:54 GMT\"}, {\"connection\", \"keep-alive\"}, {\"content-length\", \"114\"}], status_code: 400}"}
```

Using `OAuth2.Request.request!` as a model, I added a similar error handling case to `OAuth2.Client.get_token!`. Now the error raised looks like:

```
[error] #PID<0.1063.0> running ExampleOAuth2Web.Endpoint terminated
Server: oauth2.example.dev:80 (http)
Request: POST /
** (exit) an exception was raised:
    ** (OAuth2.Error) Server responded with status: 400

Headers:

www-authenticate: OAuth "Facebook Platform" "invalid_client" "Missing client_id parameter."
access-control-allow-origin: *
pragma: no-cache
cache-control: no-store
x-fb-rev: 3349509
content-type: application/json
x-fb-trace-id: CIc8eDTN/BC
facebook-api-version: v2.8
expires: Sat, 01 Jan 2000 00:00:00 GMT
x-fb-debug: wJzExwqDXtAkHKtBNo4xKE21zBO730qctNXaP9A7bqenLRuTkGq109qvx8iOy063OiE3uVunf/Mt1trqvhuwVg==
date: Thu, 05 Oct 2017 15:40:21 GMT
connection: keep-alive
content-length: 115

Body:

%{"error" => %{"code" => 101, "fbtrace_id" => "CIc8eDTN/BC", "message" => "Missing client_id parameter.", "type" => "OAuthException"}}

        (oauth2) lib/oauth2/client.ex:249: OAuth2.Client.get_token!/4
```

* Add test

* Additional test coverage

lib/oauth2/client.ex

@@ -244,8 +244,21 @@ defmodule OAuth2.Client do
   @spec get_token!(t, params, headers, Keyword.t) :: Client.t | Error.t
   def get_token!(client, params \\ [], headers \\ [], opts \\ []) do
     case get_token(client, params, headers, opts) do
-      {:ok, client} -> client
-      {:error, error} -> raise error
+      {:ok, client} ->
+        client
+      {:error, %Response{status_code: code, headers: headers, body: body}} ->
+        raise %Error{reason: """
+        Server responded with status: #{code}
+
+        Headers:
+
+        #{Enum.reduce(headers, "", fn {k, v}, acc -> acc <> "#{k}: #{v}\n" end)}
+        Body:
+
+        #{inspect body}
+        """}
+      {:error, error} ->
+        raise error
     end
   end
 

test/oauth2/client_test.exs

@@ -7,6 +7,7 @@ defmodule OAuth2.ClientTest do
   import OAuth2.TestHelpers
 
   alias OAuth2.Client
+  alias OAuth2.Response
 
   setup do
     server = Bypass.open
@@ -59,6 +60,24 @@ defmodule OAuth2.ClientTest do
     assert token.access_token == "test1234"
   end
 
+  test "get_token, get_token! when response error", %{client: client, server: server} do
+    code = [code: "code1234"]
+    headers = [{"accept", "application/json"}]
+
+    bypass server, "POST", "/oauth/token", fn conn ->
+      assert conn.query_string == ""
+      send_resp(conn, 500, ~s({"error":"missing_client_id"}))
+    end
+
+    assert {:error, error} = Client.get_token(client, code, headers)
+    assert %Response{body: body, status_code: 500} = error
+    assert body == %{"error" => "missing_client_id"}
+
+    assert_raise OAuth2.Error, ~r/Body/, fn ->
+      Client.get_token!(client, code, headers)
+    end
+  end
+
   test "refresh_token and refresh_token! with a POST", %{server: server, client_with_token: client} do
     bypass server, "POST", "/oauth/token", fn conn ->
       assert get_req_header(conn, "authorization") == []
@@ -124,6 +143,14 @@ defmodule OAuth2.ClientTest do
     assert {"content-type", "application/xml"} = List.keyfind(client.headers, "content-type", 0)
   end
 
+  test "basic_auth", %{client: client} do
+    %OAuth2.Client{client_id: id, client_secret: secret} = client
+    client = basic_auth(client)
+
+    assert {"authorization", value} = List.keyfind(client.headers, "authorization", 0)
+    assert value == "Basic " <> Base.encode64(id <> ":" <> secret)
+  end
+
   ## GET
 
   test "GET", %{server: server, client_with_token: client} do