backend-app-api: improve obo not supported error

Signed-off-by: Vincenzo Scamporlino <vincenzos@spotify.com>

packages/backend-app-api/src/services/implementations/auth/authServiceFactory.test.ts

@@ -384,7 +384,7 @@ describe('authServiceFactory', () => {
         targetPluginId: 'kubernetes',
       }),
     ).rejects.toThrow(
-      "Unable to call 'kubernetes' plugin on behalf of user, because the target plugin does not support on-behalf-of tokens",
+      "Unable to call 'kubernetes' plugin on behalf of user, because the target plugin does not support on-behalf-of tokens or the plugin doesn't exist",
     );
   });
 });

packages/backend-app-api/src/services/implementations/auth/authServiceFactory.ts

@@ -240,7 +240,7 @@ class DefaultAuthService implements AuthService {
 
         if (this.userTokenHandler.isLimitedUserToken(token)) {
           throw new AuthenticationError(
-            `Unable to call '${targetPluginId}' plugin on behalf of user, because the target plugin does not support on-behalf-of tokens`,
+            `Unable to call '${targetPluginId}' plugin on behalf of user, because the target plugin does not support on-behalf-of tokens or the plugin doesn't exist`,
           );
         }
         return { token };