(Objective-C) Get Google API Access Token using JSON Private Key using NIST Time Server Date/Time

Demonstrates how to get a Google API access token using a JSON service account private key, using the NIST time server date/time rather than the local system date/time.

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

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

// First, let's get the current date/time from time-c.nist.gov
CkoSocket *socket = [[CkoSocket alloc] init];

// Connect to an NIST time server and read the current date/time
int maxWaitMs = 8000;
BOOL useTls = NO;
BOOL success = [socket Connect: @"time-c.nist.gov" port: [NSNumber numberWithInt: 37] ssl: useTls maxWaitMs: [NSNumber numberWithInt: maxWaitMs]];
if (success != YES) {
    NSLog(@"%@",socket.LastErrorText);
    return;
}

// The time server will send a big-endian 32-bit integer representing
// the number of seconds since since 00:00 (midnight) 1 January 1900 GMT.
// The ReceiveInt32 method will receive a 4-byte integer, but returns
// YES or NO to indicate success.  If successful, the integer
// is obtained via the ReceivedInt property.
BOOL bigEndian = YES;
success = [socket ReceiveInt32: bigEndian];
if (success != YES) {
    NSLog(@"%@",socket.LastErrorText);
    return;
}

CkoDateTime *dt = [[CkoDateTime alloc] init];
[dt SetFromNtpTime: socket.ReceivedInt];

// Show the current local date/time
BOOL bLocalTime = YES;
NSLog(@"%@%@",@"Current local date/time: ",[dt GetAsRfc822: bLocalTime]);

maxWaitMs = 10;
[socket Close: [NSNumber numberWithInt: maxWaitMs]];

// ------------------------------------------------------------------------
// OK, we have the current date/time.  We'll use it to set the IAT property
// in the code below.

// First load the JSON key into a string.
CkoFileAccess *fac = [[CkoFileAccess alloc] init];
NSString *jsonKey = [fac ReadEntireTextFile: @"qa_data/googleApi/ChilkatTest-ab2ecd52ef98.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": "chilkattest-1350",
// 	  "private_key_id": "fa2e36ee26986eab628b59868af8bec1d1c64c38",
// 	  "private_key": "-----BEGIN PRIVATE KEY-----\nMIIEvgIjFa...28N64N2n1E4FYzBZjSdy\n-----END PRIVATE KEY-----\n",
// 	  "client_email": "598922945226-00rb0ppfg0sndajo6bhvd4v17jtj2d3a@developer.gserviceaccount.com",
// 	  "client_id": "598922945226-00rb0ppfg0snd9jo7bhvd4v17jtj2d3a.apps.googleusercontent.com",
// 	  "auth_uri": "https://accounts.google.com/o/oauth2/auth",
// 	  "token_uri": "https://accounts.google.com/o/oauth2/token",
// 	  "auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs",
// 	  "client_x509_cert_url": "https://www.googleapis.com/robot/v1/metadata/x509/598922945226-00rb0ppfg0sndajo6bhvd4v17jtj2d3a%40developer.gserviceaccount.com"
// 	}

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

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

// 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 = @"";

// ------------------------------------------------------------------------
// Set the IAT using the date/time from the NIST time server.
int unixTime = [dt GetAsUnixTime: NO];
NSLog(@"%@%d",@"unixTime = ",unixTime);
gAuth.Iat = [NSNumber numberWithInt: unixTime];

// 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);