(Objective-C) Google Photos Refresh Access Token

Demonstrates how to refresh a Google Access Token. Refreshing an oauth2 access token does not need to display an interactive browser like when originally getting the OAuth2 access token for the 1st time. Your application can do it automatically without user interaction.

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#import <CkoJsonObject.h>
#import <CkoOAuth2.h>
#import <CkoStringBuilder.h>

// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

// It is assumed we previously obtained an OAuth2 access token.
// This example loads the JSON access token file 
// saved by this example: Get Google Photos OAuth2 Access Token

CkoJsonObject *jsonToken = [[CkoJsonObject alloc] init];
BOOL success = [jsonToken LoadFile: @"qa_data/tokens/googlePhotos.json"];
if (success != YES) {
    NSLog(@"%@",@"Failed to load googlePhotos.json");
    return;
}

// The access token JSON looks like this:

// {
//   "access_token": "ya29.GlamBqWR6cp8lEfJMmTHVEua45912XLKoq4djyHl_Z3CEIzsPLIZkJSGie5oOrbaggy1rjJHn1zW5bjqSesGr5MEYIp9Hx-0CuvjVYf8srg2jeaDMwMACvzemp43",
//   "expires_in": 3600,
//   "refresh_token": "1/rl6k16nysDl9Bp1EhRH9F1WyRIoiSQAvko49Z4yY694MT5V1QXLj2ibNZGaRgek0",
//   "scope": "https://www.googleapis.com/auth/photoslibrary",
//   "token_type": "Bearer"
// }

CkoOAuth2 *oauth2 = [[CkoOAuth2 alloc] init];

oauth2.TokenEndpoint = @"https://www.googleapis.com/oauth2/v4/token";

// Replace these with actual values.
oauth2.ClientId = @"GOOGLE-CLIENT-ID";
oauth2.ClientSecret = @"GOOGLE-CLIENT-SECRET";

// Get the "refresh_token"
oauth2.RefreshToken = [jsonToken StringOf: @"refresh_token"];

// Send the HTTP POST to refresh the access token..
success = [oauth2 RefreshAccessToken];
if (success != YES) {
    NSLog(@"%@",oauth2.LastErrorText);
    return;
}

// The response contains a new access token, but we must keep
// our existing refresh token for when we need to refresh again in the future.
[jsonToken UpdateString: @"access_token" value: oauth2.AccessToken];

// Save the new JSON access token response to a file.
CkoStringBuilder *sbJson = [[CkoStringBuilder alloc] init];
jsonToken.EmitCompact = NO;
[jsonToken EmitSb: sbJson];
[sbJson WriteFile: @"qa_data/tokens/googlePhotos.json" charset: @"utf-8" emitBom: NO];

NSLog(@"%@",@"OAuth2 authorization granted!");
NSLog(@"%@%@",@"New Access Token = ",oauth2.AccessToken);