(Objective-C) HMRC OAuth2 Access Token

Demonstrates how to get an HMRC OAuth2 access token from a desktop (installed) application or script. This example gets an HMRC MTD VAT read/write access token.

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#import <CkoOAuth2.h>
#import <NSString.h>
#import <CkoHttp.h>
#import <CkoJsonObject.h>
#import <CkoDateTime.h>
#import <CkoFileAccess.h>

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

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

// This should be the port in the localhost callback URL for your app.
// Important: Make sure the callback URI in your HMRC developer app 
// is exactly "http://localhost:3017/".  Don't forget the ending "/" char.
// The callback URL would look like "http://localhost:3017/" if the port number is 3017.

// IMPORTANT: Don't forget to setup your HMRC application to use the Redirect URI "http://localhost:3017/" as shown
// here: Configure Redirect URI for HMRC application
oauth2.ListenPort = [NSNumber numberWithInt:3017];

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

// The scopes are documented in the HMRC reference documentation for each API.
// This example gets a read/write access token for the HMRC MTD VAT API.
oauth2.Scope = @"read:vat write:vat";

// Begin the OAuth2 three-legged flow.  This returns a URL that should be loaded in a browser.
NSString *url = [oauth2 StartAuth];
if (oauth2.LastMethodSuccess != YES) {
    NSLog(@"%@",oauth2.LastErrorText);
    return;
}

CkoHttp *http = [[CkoHttp alloc] init];

// At this point, your application should load the URL in a browser.
// For example, 
// in C#: System.Diagnostics.Process.Start(url);
// in Java: Desktop.getDesktop().browse(new URI(url));
// in VBScript: Set wsh=WScript.CreateObject("WScript.Shell")
//              wsh.Run url
// in Xojo: ShowURL(url)  (see http://docs.xojo.com/index.php/ShowURL)
// in Dataflex: Runprogram Background "c:\Program Files\Internet Explorer\iexplore.exe" sUrl        
// The GitHub account owner would interactively accept or deny the authorization request.

// Add the code to load the url in a web browser here...
// Add the code to load the url in a web browser here...
// Add the code to load the url in a web browser here...

// Now wait for the authorization.
// We'll wait for a max of 120 seconds.
int numMsWaited = 0;
while ((numMsWaited < 120000) && ([oauth2.AuthFlowState intValue] < 3)) {
    [oauth2 SleepMs: [NSNumber numberWithInt: 100]];
    numMsWaited = numMsWaited + 100;
}

// If there was no response from the browser within 30 seconds, then 
// the AuthFlowState will be equal to 1 or 2.
// 1: Waiting for Redirect. The OAuth2 background thread is waiting to receive the redirect HTTP request from the browser.
// 2: Waiting for Final Response. The OAuth2 background thread is waiting for the final access token response.
// In that case, cancel the background task started in the call to StartAuth.
if ([oauth2.AuthFlowState intValue] < 3) {
    [oauth2 Cancel];
    NSLog(@"%@",@"No response from the browser!");
    return;
}

// Check the AuthFlowState to see if authorization was granted, denied, or if some error occurred
// The possible AuthFlowState values are:
// 3: Completed with Success. The OAuth2 flow has completed, the background thread exited, and the successful JSON response is available in AccessTokenResponse property.
// 4: Completed with Access Denied. The OAuth2 flow has completed, the background thread exited, and the error JSON is available in AccessTokenResponse property.
// 5: Failed Prior to Completion. The OAuth2 flow failed to complete, the background thread exited, and the error information is available in the FailureInfo property.
if ([oauth2.AuthFlowState intValue] == 5) {
    NSLog(@"%@",@"OAuth2 failed to complete.");
    NSLog(@"%@",oauth2.FailureInfo);
    return;
}

if ([oauth2.AuthFlowState intValue] == 4) {
    NSLog(@"%@",@"OAuth2 authorization was denied.");
    NSLog(@"%@",oauth2.AccessTokenResponse);
    return;
}

if ([oauth2.AuthFlowState intValue] != 3) {
    NSLog(@"%@%d",@"Unexpected AuthFlowState:",[oauth2.AuthFlowState intValue]);
    return;
}

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

// Get the full JSON response:
CkoJsonObject *json = [[CkoJsonObject alloc] init];
[json Load: oauth2.AccessTokenResponse];
json.EmitCompact = NO;
NSLog(@"%@",[json Emit]);

// The JSON response looks 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": "..."
// }

// 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 ([json HasMember: @"expires_on"] != YES) {
    CkoDateTime *dtExpire = [[CkoDateTime alloc] init];
    [dtExpire SetFromCurrentSystemTime];
    [dtExpire AddSeconds: [json IntOf: @"expires_in"]];
    [json AppendString: @"expires_on" value: [dtExpire GetAsUnixTimeStr: NO]];
}

NSLog(@"%@",[json Emit]);

// Save the JSON to a file for future requests.
CkoFileAccess *fac = [[CkoFileAccess alloc] init];
[fac WriteEntireTextFile: @"qa_data/tokens/hmrc.json" fileData: [json Emit] charset: @"utf-8" includePreamble: NO];