(Objective-C) Get Access Token for Google Tasks using Service Account JSON Key

Demonstrates how to get an access token for the Google Tasks API using a Service Account JSON 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/googleSvcAccountKeys/ChilkatCloud-48f7737c7505.json" charset: @"utf-8"];
if (fac.LastMethodSuccess != YES) {
    NSLog(@"%@",fac.LastErrorText);
    return;
}

// A JSON private key should look like this:

// {
//   "type": "service_account",
//   "project_id": "chilkatcloud",
//   "private_key_id": "48f7737c7505bb88eee6a20d09993e10605d466e",
//   "private_key": "-----BEGIN PRIVATE KEY----- ... -----END PRIVATE KEY-----\n",
//   "client_email": "pip-564@chilkatcloud.iam.gserviceaccount.com",
//   "client_id": "109982228323456925225",
//   "auth_uri": "https://accounts.google.com/o/oauth2/auth",
//   "token_uri": "https://oauth2.googleapis.com/token",
//   "auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs",
//   "client_x509_cert_url": "https://www.googleapis.com/robot/v1/metadata/x509/pip-564%40chilkatcloud.iam.gserviceaccount.com"
// }

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

// Choose the scope for read/write access.
gAuth.Scope = @"https://www.googleapis.com/auth/tasks";

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

gAuth.SubEmailAddress = @"";

// Connect to www.googleapis.com using TLS
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);

// Save our access token to a file.
success = [fac WriteEntireTextFile: @"qa_data/tokens/googleTasks.txt" fileData: gAuth.AccessToken charset: @"utf-8" includePreamble: NO];