(Objective-C) Get a Google Drive Access Token using a JSON Private Key

Demonstrates how to get a Google Drive API access token using a JSON service account private key.

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#import <CkoFileAccess.h>
#import <NSString.h>
#import <CkoAuthGoogle.h>
#import <CkoSocket.h>

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

// First load the JSON key into a string.
CkoFileAccess *fac = [[CkoFileAccess alloc] init];
NSString *jsonKey = [fac ReadEntireTextFile: @"qa_data/googleApi/chilkatcloud-b8826e030499.json" charset: @"utf-8"];
if (fac.LastMethodSuccess != YES) {
    NSLog(@"%@",fac.LastErrorText);
    return;
}

CkoAuthGoogle *gAuth = [[CkoAuthGoogle alloc] init];
gAuth.JsonKey = jsonKey;

// Choose a scope.
gAuth.Scope = @"https://www.googleapis.com/auth/drive";

// Request an access token that is valid for this many seconds.
gAuth.ExpireNumSeconds = [NSNumber numberWithInt:3600];

// If the application is requesting delegated access:
// The email address of the user for which the application is requesting delegated access,
// then set the email address here. (Otherwise leave it empty.)
gAuth.SubEmailAddress = @"";

// Connect to www.googleapis.com using TLS (TLS 1.2 is the default.)
// The Chilkat socket object is used so that the connection can be established
// through proxies or an SSH tunnel if desired.
CkoSocket *tlsSock = [[CkoSocket alloc] init];
BOOL success = [tlsSock Connect: @"www.googleapis.com" port: [NSNumber numberWithInt: 443] ssl: YES maxWaitMs: [NSNumber numberWithInt: 5000]];
if (success != YES) {
    NSLog(@"%@",tlsSock.LastErrorText);
    return;
}

// Send the request to obtain the access token.
success = [gAuth ObtainAccessToken: tlsSock];
if (success != YES) {
    NSLog(@"%@",gAuth.LastErrorText);
    return;
}

// Examine the access token:
NSLog(@"%@%@",@"Access Token: ",gAuth.AccessToken);