Add resaturation function for user instances

Author: sam-gc

packages-exp/auth-exp/src/core/index.ts

@@ -197,6 +197,7 @@ export {
 export { getIdToken, getIdTokenResult } from './user/id_token_result';
 export { unlink } from './user/link_unlink';
 export { getAdditionalUserInfo } from './user/additional_user_info';
+export { userFromJSON } from './user/user_impl';
 
 // Non-optional user methods.
 export { reload } from './user/reload';

packages-exp/auth-exp/src/core/user/user_impl.ts

@@ -26,6 +26,7 @@ import { FinalizeMfaResponse } from '../../api/authentication/mfa';
 import { Auth } from '../../model/auth';
 import { IdTokenResponse } from '../../model/id_token';
 import { MutableUserInfo, User, UserParameters } from '../../model/user';
+import { _castAuth } from '../auth/auth_impl';
 import { AuthErrorCode } from '../errors';
 import { PersistedBlob } from '../persistence';
 import { _assert } from '../util/assert';
@@ -317,3 +318,7 @@ export class UserImpl implements User {
     return user;
   }
 }
+
+export function userFromJSON(auth: externs.Auth, json: string): externs.User {
+  return UserImpl._fromJSON(_castAuth(auth), JSON.parse(json));
+}