GTLRPeopleServiceQuery_PeopleGet *getDataQuery =
[GTLRPeopleServiceQuery_PeopleGet queryWithResourceName: @"people/me"];
    [getDataQuery setPersonFields:@"genders,birthdays"];

    GTLRPeopleServiceService *gService = [[GTLRPeopleServiceService alloc] init];
    [gService setAPIKey:@"APIKEYHERE"];
    [gService executeQuery: getDataQuery delegate:self didFinishSelector:@selector(getCreatorFromTicket:finishedWithObject:error:)];


-(void)getCreatorFromTicket:(GTLRServiceTicket *) ticket finishedWithObject: (GTLRPeopleService_Person *) finishedWithObject error: (NSError *)error
{
if (error != nil) {
    NSLog(@"Error is %@", error.localizedDescription);
}

NSLog(@"Response is %@", finishedWithObject);
}

The request does not have valid authentication credentials.