Fix keychain issues (#3239)

Author: renkelvin

Firebase/Auth/Source/Auth/FIRAuth.m

@@ -2020,13 +2020,13 @@ - (nullable FIRUser *)getStoredUserForAccessGroup:(NSString *_Nullable)accessGro
     NSKeyedUnarchiver *unarchiver =
         [[NSKeyedUnarchiver alloc] initForReadingWithData:encodedUserData];
     user = [unarchiver decodeObjectOfClass:[FIRUser class] forKey:userKey];
-    user.auth = self;
   } else {
     user = [self.storedUserManager getStoredUserForAccessGroup:self.userAccessGroup
                                              projectIdentifier:self.app.options.APIKey
                                                          error:outError];
   }
 
+  user.auth = self;
   return user;
 }
 

Firebase/Auth/Source/User/FIRUser.m

@@ -332,7 +332,7 @@ - (nullable instancetype)initWithCoder:(NSCoder *)aDecoder {
   FIRUserMetadata *metadata =
       [aDecoder decodeObjectOfClass:[FIRUserMetadata class] forKey:kMetadataCodingKey];
   NSString *APIKey =
-      [aDecoder decodeObjectOfClass:[FIRUserMetadata class] forKey:kAPIKeyCodingKey];
+      [aDecoder decodeObjectOfClass:[NSString class] forKey:kAPIKeyCodingKey];
   if (!userID || !tokenService) {
     return nil;
   }