(Objective-C) Azure AD Service-to-service access token request

Send an Azure AD service-to-service token request to get an access token using a shared secret.

For more information, see https://docs.microsoft.com/en-us/azure/active-directory/develop/v1-oauth2-client-creds-grant-flow#service-to-service-access-token-request

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#import <CkoHttp.h>
#import <CkoHttpRequest.h>
#import <CkoHttpResponse.h>
#import <CkoJsonObject.h>
#import <NSString.h>

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

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

// To see the exact HTTP request sent and the response, set the SessionLogFilename property:
http.SessionLogFilename = @"qa_output/chilkatHttpLog.txt";

CkoHttpRequest *req = [[CkoHttpRequest alloc] init];

// Set the following request params:
// grant_type 	required 	Specifies the requested grant type. In a Client Credentials Grant flow, the value must be client_credentials.
// 
// client_id 	required 	Specifies the Azure AD client id of the calling web service. 
//     To find the calling application's client ID, in the Azure portal, click Azure Active Directory, click App registrations, click the application. 
//     The client_id is the Application ID
// 
// client_secret 	required 	Enter a key registered for the calling web service or daemon application in Azure AD. 
//     To create a key, in the Azure portal, click Azure Active Directory, click App registrations, click the application, click Settings, click Keys, and add a Key.
//     URL-encode this secret when providing it.
// 
// resource 	required 	Enter the App ID URI of the receiving web service. To find the App ID URI, in the Azure portal, click Azure Active Directory, 
//     click App registrations, click the service application, and then click Settings and Properties.

[req AddParam: @"grant_type" value: @"client_credentials"];
[req AddParam: @"client_id" value: @"MY_CLIENT_ID"];
[req AddParam: @"client_secret" value: @"MY_CLIENT_SECRET"];
[req AddParam: @"resource" value: @"https://service.contoso.com/"];

// The URL passed to PostUrlEncoded has this form:   https://login.microsoftonline.com/<tenant_id>/oauth2/token
CkoHttpResponse *resp = [http PostUrlEncoded: @"https://login.microsoftonline.com/<tenant_id>/oauth2/token" req: req];
if (http.LastMethodSuccess == NO) {
    NSLog(@"%@",http.LastErrorText);
    return;
}

int respStatusCode = [resp.StatusCode intValue];
NSLog(@"%@%d",@"Response Status Code = ",respStatusCode);

CkoJsonObject *json = [[CkoJsonObject alloc] init];
json.EmitCompact = NO;
[json Load: resp.BodyStr];
NSLog(@"%@",@"Response JSON:");
NSLog(@"%@",[json Emit]);

if (respStatusCode >= 400) {
    NSLog(@"%@",@"Response Header:");
    NSLog(@"%@",resp.Header);
    NSLog(@"%@",@"Failed.");

    return;
}

// Sample response:

// {
//   "token_type": "Bearer",
//   "expires_in": "3599",
//   "ext_expires_in": "3599",
//   "expires_on": "1570059833",
//   "not_before": "1570055933",
//   "resource": "https://adminchilkatsoft.onmicrosoft.com/eb1b8ced-76b7-4845-aec5-d3e91776e345",
//   "access_token": "eyJ0eXAiO ... pmgw"
// }

// To get the items from the JSON....
NSString *token_type = [json StringOf: @"token_type"];
NSString *expires_in = [json StringOf: @"expires_in"];
NSString *ext_expires_in = [json StringOf: @"ext_expires_in"];
NSString *expires_on = [json StringOf: @"expires_on"];
NSString *not_before = [json StringOf: @"not_before"];
NSString *resource = [json StringOf: @"resource"];
NSString *access_token = [json StringOf: @"access_token"];