(Objective-C) Refresh HMRC OAuth2 Access Token

Demonstrates how to refresh an HMRC access token.

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

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

// See Get HMRC Access Token 
// for sample code showing how to obtain a HMRC access token for desktop apps.

// It is assumed we previously obtained an OAuth2 access token for HMRC.

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

// The access token JSON looks something like this:

// {
//   "token_type": "Bearer",
//   "scope": "user_impersonation",
//   "expires_in": "3599",
//   "ext_expires_in": "0",
//   "expires_on": "1524783438",
//   "not_before": "1524779538",
//   "resource": "https://mydomain.api.crm.dynamics.com",
//   "access_token": "...",
//   "refresh_token": "...",
//   "id_token": "..."
// }

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

oauth2.TokenEndpoint = @"https://test-api.service.hmrc.gov.uk/oauth/token";

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

// Load the access token response into the json object 
[jsonToken Load: oauth2.AccessTokenResponse];

// If an "expires_on" member does not exist, then add the JSON member by
// getting the current system date/time and adding the "expires_in" seconds.
// This way we'll know when the token expires.
if ([jsonToken HasMember: @"expires_on"] == NO) {
    CkoDateTime *dtExpire = [[CkoDateTime alloc] init];
    [dtExpire SetFromCurrentSystemTime];
    [dtExpire AddSeconds: [jsonToken IntOf: @"expires_in"]];
    [jsonToken AppendString: @"expires_on" value: [dtExpire GetAsUnixTimeStr: NO]];
}

// Save the new JSON access token response to a file.
// The access + refresh tokens contained in this JSON will be needed for the next refresh.
CkoStringBuilder *sbJson = [[CkoStringBuilder alloc] init];
jsonToken.EmitCompact = NO;
[jsonToken EmitSb: sbJson];
[sbJson WriteFile: @"qa_data/tokens/hmrc.json" charset: @"utf-8" emitBom: NO];

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