[various] added FlutterAppAuthOAuthError to hold standard error codes that apps can reference

flutter_appauth/CHANGELOG.md

@@ -3,6 +3,7 @@
 * **Breaking change** all methods have now been made to return non-nullable types
 * [Android] updated plugin to specify `Theme.AppCompat.Translucent.NoTitleBar` as the theme for the `RedirectUriReceiverActivity` from the AppAuth Android SDK. This is to fix a crash raised with issues [#362](https://github.com/MaikuB/flutter_appauth/issues/362) and [#515](https://github.com/MaikuB/flutter_appauth/issues/515)
 * [iOS][macOS] bumped AppAuth iOS dependency to 1.7.5
+* Added `FlutterAppAuthOAuthError` class that contains string constants representing OAuth 2.0 error codes defined by the [specification](https://datatracker.ietf.org/doc/html/rfc6749#section-5.2).
 * Updated API docs with more details
 * Updated readme with more details on essential knowledge and links to OAuth 2.0 specifications
 

flutter_appauth_platform_interface/CHANGELOG.md

@@ -2,6 +2,7 @@
 
 * **Breaking change** all methods have now been made to return non-nullable types
 * Updated API docs with more details
+* Added `FlutterAppAuthOAuthError` class that contains string constants representing OAuth 2.0 error codes defined by the [specification](https://datatracker.ietf.org/doc/html/rfc6749#section-5.2).
 
 ## [7.0.0-dev.2]
 

flutter_appauth_platform_interface/lib/src/errors.dart

@@ -37,6 +37,13 @@ class FlutterAppAuthPlatformErrorDetails {
   /// For 400 errors from the authorization server, this is corresponds to the
   /// `error` parameter as defined in the OAuth 2.0 framework [here](https://datatracker.ietf.org/doc/html/rfc6749#section-5.2).
   /// Otherwise a short error describing what happened.
+  ///
+  /// The [FlutterAppAuthOAuthError] class contains string constants for
+  /// the standard error codes that could used by applications to determine the
+  /// nature of the error.
+  ///
+  /// Note that authorization servers may return custom error codes that are not
+  /// defined in the OAuth 2.0 framework.
   final String? error;
 
   /// Short, human readable error description.
@@ -133,3 +140,17 @@ class FlutterAppAuthPlatformException extends PlatformException {
   /// Details of the error from the underlying platform's AppAuth SDK.
   final FlutterAppAuthPlatformErrorDetails platformErrorDetails;
 }
+
+/// Represents OAuth error codes that can be returned by the authorization
+/// server.
+///
+/// These are the standard error codes defined in the OAuth 2.0 framework
+/// [here](https://datatracker.ietf.org/doc/html/rfc6749#section-5.2).
+class FlutterAppAuthOAuthError {
+  static const String invalidRequest = 'invalid_request';
+  static const String invalidClient = 'invalid_client';
+  static const String invalidGrant = 'invalid_grant';
+  static const String unauthorizedClient = 'unauthorized_client';
+  static const String unsupportedGrantType = 'unsupported_grant_type';
+  static const String invalidScope = 'invalid_scope';
+}