403 Error - Thats an error. Error: disallowed_useragent

I am trying to authorise a user for Google calendar API inside an IOS app. I am using the OAuth2 feature of Google to authenticate users. Authorisation page opens with a 403 error with the description:

This user-agent is not permitted to make OAuth authorisation request to Google as it is classified as an embedded user-agent (also known as a web-view). Per our policy, only browsers are permitted to make authorisation requests to Google. We offer several libraries and samples for native apps to perform authorisation request in browser.

I followed the same procedure which is mentioned in this link: https://developers.google.com/google-apps/calendar/quickstart/ios

Rather than seeing my code, it's better to look at this link: https://developers.google.com/google-apps/calendar/quickstart/ios because I copy-pasted the same thing in my application.

below are my clientId and keyChainItemName:

static NSString *const kKeychainItemName = @"Google Calendar API";
static NSString *const kClientID = @"954370342601-sgl8k0jrbqdeagea9v6vfu3tspte96ci.apps.googleusercontent.com";

In my case I was using native web view to login with Google, I find out the way that you should provide user agent to webview it was worked for me. Try below code I am sure it will worked.

Add the code in application didFinishLaunchingWithOptions

Objective C

 NSDictionary *dictionary = [NSDictionary dictionaryWithObjectsAndKeys:@"Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36", @"UserAgent", nil];
 [[NSUserDefaults standardUserDefaults] registerDefaults:dictionary];

Swift 3.0

let dictionary = NSDictionary(object: "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36", forKey: "UserAgent" as NSCopying)
UserDefaults.standard.register(defaults: dictionary)

<preference name="OverrideUserAgent" value="Mozilla/5.0 Google" />

I also face this issue on my cordova project. You can try this: Just add this to your config.xml, worked for me.