(Objective-C) Get Access Token using a Pre-Created JSON Web Token

Demonstrates how to get an access token using a pre-created JSON Web Token (JWT).

For more information, see https://developer.abnamro.com/get-started#headingFive

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

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

// We're going to duplicate this CURL statement:
// curl -X POST https://api-sandbox.abnamro.com/v1/oauth/token \
// -H "Content-Type: application/x-www-form-urlencoded" \
// -H "API-Key: xxxxxx" \
// -d 'client_assertion_type=urn:ietf:params:oauth:client-assertion-type:jwt-bearer&grant_type=client_credentials&client_assertion=eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiJ4eHh4eHgiLCJleHAiOiIxNDk5OTQ3NjY4IiwiaXNzIjoibWUiLCJhdWQiOiJodHRwczovL2F1dGgtc2FuZGJveC5hYm5hbXJvLmNvbS9vYXV0aC90b2tlbiJ9.jGwHKG_YjgKpR8NPpaLu6nJ97obeP2vcxg6fOWBKdJ0&scope=tikkie'

// Load our pre-creaed private key PEM file.
// Note: Please share your public key along with your app name and developer email id at api.support@nl.abnamro.com. 
// Token generation will not work unless public key is associated with your app.
CkoPrivateKey *privkey = [[CkoPrivateKey alloc] init];

BOOL success = [privkey LoadPemFile: @"qa_data/pem/abnAmroPrivateKey.pem"];
if (success == NO) {
    NSLog(@"%@",privkey.LastErrorText);
    return;
}

// Create the JWT.
CkoJwt *jwt = [[CkoJwt alloc] init];

// Create the header:
// {
//     "typ": "JWT",
//     "alg": "RS256"
// }
CkoJsonObject *jsonHeader = [[CkoJsonObject alloc] init];
[jsonHeader UpdateString: @"typ" value: @"JWT"];
[jsonHeader UpdateString: @"alg" value: @"RS256"];

// Create the payload:
// {
//     "nbf": 1499947668,
//     "exp": 1499948668,
//     "iss": "me",
//     "sub": "anApiKey",
//     "aud": "https://auth-sandbox.abnamro.com/oauth/token"
// }
CkoJsonObject *jsonPayload = [[CkoJsonObject alloc] init];

int curDateTime = [[jwt GenNumericDate: [NSNumber numberWithInt: 0]] intValue];

// Set the "not process before" timestamp to now.
success = [jsonPayload AddIntAt: [NSNumber numberWithInt: -1] name: @"nbf" value: [NSNumber numberWithInt: curDateTime]];

// Set the timestamp defining an expiration time (end time) for the token
// to be now + 1 hour (3600 seconds)
success = [jsonPayload AddIntAt: [NSNumber numberWithInt: -1] name: @"exp" value: [NSNumber numberWithInt: (curDateTime + 3600)]];

[jsonPayload UpdateString: @"iss" value: @"me"];
[jsonPayload UpdateString: @"sub" value: @"anApiKey"];
[jsonPayload UpdateString: @"aud" value: @"https://auth-sandbox.abnamro.com/oauth/token"];

// Produce the smallest possible JWT:
jwt.AutoCompact = YES;

NSString *jwtStr = [jwt CreateJwtPk: [jsonHeader Emit] payload: [jsonPayload Emit] key: privkey];
if (jwt.LastMethodSuccess != YES) {
    NSLog(@"%@",jwt.LastErrorText);
    return;
}

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

CkoHttpRequest *req = [[CkoHttpRequest alloc] init];
[req AddParam: @"client_assertion_type" value: @"urn:ietf:params:oauth:client-assertion-type:jwt-bearer"];
[req AddParam: @"grant_type" value: @"client_credentials"];
[req AddParam: @"client_assertion" value: jwtStr];
[req AddParam: @"scope" value: @"tikkie"];

CkoHttpResponse *resp = [http PostUrlEncoded: @"https://api-sandbox.abnamro.com/v1/oauth/token" req: req];
if (http.LastMethodSuccess == NO) {
    NSLog(@"%@",http.LastErrorText);
    return;
}

if ([resp.StatusCode intValue] != 200) {
    NSLog(@"%@",resp.BodyStr);

    return;
}

// Get the JSON result:
// {
//     "access_token": "{your access token}",
//     "expires_in": "{duration of validity in seconds}",
//     "scope": "{scope(s) for which the access token is valid}",
//     "token_type": "{it is always Bearer}"
// }
CkoJsonObject *json = [[CkoJsonObject alloc] init];
[json Load: resp.BodyStr];
NSLog(@"%@%@",@"access_token: ",[json StringOf: @"access_token"]);
NSLog(@"%@%@",@"token_type: ",[json StringOf: @"token_type"]);
NSLog(@"%@%@",@"expires_in: ",[json StringOf: @"expires_in"]);
NSLog(@"%@%@",@"scope: ",[json StringOf: @"scope"]);