Replace TokenResponse generic with associated type

This change slightly simplifies types throughout this crate by removing
a generic type parameter in many places that already have a generic type
representing a `TokenResponse`.

BREAKING CHANGES:
 - Removes `TT` type parameter from `TokenResponse` and
   `TokenIntrospectionResponse` traits trait and adds a `TokenType`
   associated type to each trait.
 - Removes (now-redundant) `TT` type parameter from `Client` and each
   `*Response` type

UPGRADE.md

@@ -200,6 +200,22 @@ the root. For example, if you were previously importing
 `oauth2::devicecode::DeviceAuthorizationResponse`, instead import
 `oauth2::DeviceAuthorizationResponse`.
 
+### Replace `TT` generic type parameter in `TokenResponse` with associated type
+
+Previously, the `TokenResponse` and `TokenIntrospectionResponse` traits had a generic type
+parameter `TT: TokenType`. This has been replaced with an associated type called `TokenType`.
+Uses of `BasicTokenResponse` and `BasicTokenIntrospectionResponse` should continue to work without
+changes, but custom implementations of either trait will need to be updated to replace the type
+parameter with an associated type.
+
+#### Remove `TT` generic type parameter from `Client` and each `*Request` type
+
+Removing the `TT` generic type parameter from `TokenResponse` (see above) made the `TT` parameters
+to `Client` and each `*Request` (e.g., `CodeTokenRequest`) redundant. Consequently, the `TT`
+parameter has been removed from each of these types. `BasicClient` should continue to work
+without any changes, but code that provides generic types for `Client` or any of the `*Response`
+types will need to be updated to remove the `TT` type parameter.
+
 ### Add `Display` to `ErrorResponse` trait
 
 To improve error messages, the

examples/wunderlist.rs

@@ -19,12 +19,12 @@ use oauth2::basic::{
     BasicTokenType,
 };
 use oauth2::reqwest;
+use oauth2::StandardRevocableToken;
 use oauth2::{
     AccessToken, AuthUrl, AuthorizationCode, Client, ClientId, ClientSecret, CsrfToken,
     EmptyExtraTokenFields, EndpointNotSet, ExtraTokenFields, RedirectUrl, RefreshToken, Scope,
     TokenResponse, TokenUrl,
 };
-use oauth2::{StandardRevocableToken, TokenType};
 use serde::{Deserialize, Serialize};
 use url::Url;
 
@@ -43,7 +43,6 @@ type SpecialClient<
 > = Client<
     BasicErrorResponse,
     SpecialTokenResponse,
-    BasicTokenType,
     BasicTokenIntrospectionResponse,
     StandardRevocableToken,
     BasicRevocationErrorResponse,
@@ -88,11 +87,11 @@ pub struct NonStandardTokenResponse<EF: ExtraTokenFields> {
     extra_fields: EF,
 }
 
-impl<EF> TokenResponse<BasicTokenType> for NonStandardTokenResponse<EF>
+impl<EF> TokenResponse for NonStandardTokenResponse<EF>
 where
     EF: ExtraTokenFields,
-    BasicTokenType: TokenType,
 {
+    type TokenType = BasicTokenType;
     /// REQUIRED. The access token issued by the authorization server.
     fn access_token(&self) -> &AccessToken {
         &self.access_token

src/basic.rs

@@ -17,7 +17,6 @@ pub type BasicClient<
 > = Client<
     BasicErrorResponse,
     BasicTokenResponse,
-    BasicTokenType,
     BasicTokenIntrospectionResponse,
     StandardRevocableToken,
     BasicRevocationErrorResponse,