feat(shorebird_code_push_protocol): Add shorebird AuthProvider (#3618)

Co-authored-by: Eric Seidel <eric@shorebird.dev>

packages/shorebird_cli/lib/src/auth/auth.dart

@@ -429,6 +429,9 @@ extension OauthValues on AuthProvider {
   oauth2.AuthEndpoints get authEndpoints => switch (this) {
     (AuthProvider.google) => const oauth2.GoogleAuthEndpoints(),
     (AuthProvider.microsoft) => MicrosoftAuthEndpoints(),
+    (AuthProvider.shorebird) => throw UnsupportedError(
+      'Shorebird auth is not yet supported in the CLI',
+    ),
   };
 
   /// The OAuth 2.0 client ID for the provider.
@@ -456,6 +459,10 @@ extension OauthValues on AuthProvider {
           /// Shorebird CLI's OAuth 2.0 identifier for Azure/Entra.
           '4fc38981-4ec4-4bd9-a755-e6ad9a413054',
         );
+      case AuthProvider.shorebird:
+        throw UnsupportedError(
+          'Shorebird auth is not yet supported in the CLI',
+        );
     }
   }
 
@@ -471,5 +478,8 @@ extension OauthValues on AuthProvider {
       // Required to get refresh tokens.
       'offline_access',
     ],
+    (AuthProvider.shorebird) => throw UnsupportedError(
+      'Shorebird auth is not yet supported in the CLI',
+    ),
   };
 }

packages/shorebird_cli/lib/src/auth/ci_token.g.dart

@@ -35,4 +35,5 @@ Map<String, dynamic> _$CiTokenToJson(CiToken instance) => <String, dynamic>{
 const _$AuthProviderEnumMap = {
   AuthProvider.google: 'google',
   AuthProvider.microsoft: 'microsoft',
+  AuthProvider.shorebird: 'shorebird',
 };

packages/shorebird_code_push_protocol/lib/src/models/auth_provider.dart

@@ -4,7 +4,10 @@ enum AuthProvider {
   google('Google'),
 
   /// The user authenticated with their Azure/Entra account.
-  microsoft('Microsoft');
+  microsoft('Microsoft'),
+
+  /// The user authenticated via Shorebird's own auth service.
+  shorebird('Shorebird');
 
   const AuthProvider(this.displayName);