(Objective-C) Verify Okta Access Token Locally

This example demonstrates how to validate an Okta access token using Chilkat's JWT class.

For more information, see https://developer.okta.com/docs/guides/validate-access-tokens/overview/#what-to-check-when-validating-an-access-token

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#import <CkoJsonObject.h>
#import <CkoJwt.h>
#import <NSString.h>
#import <CkoStringBuilder.h>
#import <CkoPublicKey.h>

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

// This example begins with two JSON files:
// 
// 1. The access token obtained from Okta as shown in one fo these examples:  
//    Get Okta Token using Resource Owner Password Flow
// 
// 2. The Okta web keys obtained by this example:  Get Okta Web Keys
// 
// 

// Load the access token to be verified.
// It contains JSON that looks like this:
// {
//   "access_token": "eyJraWQiOiJhb ... O_eVu-kBp6g",
//   "token_type": "Bearer",
//   "expires_in": 3600,
//   "scope": "openid",
//   "id_token": "eyJraWQi ... FrL9WOuwbQtUg"
// }
// This example verifies the access_token.  (The id_token is verified in this example:  Verify Okta ID Token

CkoJsonObject *jsonToken = [[CkoJsonObject alloc] init];
BOOL success = [jsonToken LoadFile: @"qa_data/tokens/okta_access_token.json"];

// Load the public keys (Okta web keys), one of which is needed to validate.
// The web keys JSON looks like this:
// {
//   "keys": [
//     {
//       "kty": "RSA",
//       "alg": "RS256",
//       "kid": "anSaRDPfWGOSCVNZEIZB9quCbNsdsvl5uWGBzxbudWQ",
//       "use": "sig",
//       "e": "AQAB",
//       "n": "jT8uAgd5w ... euLB1HaVw"
//     },
//     {
// 	...
//     }
//   ]
// }

CkoJsonObject *jsonWebKeys = [[CkoJsonObject alloc] init];
success = [jsonWebKeys LoadFile: @"qa_data/tokens/okta_web_keys.json"];

// ------------------------
// Step 1: Get the JOSE header from the JWT.  The JOSE header contains JSON.  One of the JSON members will be the key ID "kid" which identifies the web key to be used for validation.
// 
CkoJwt *jwt = [[CkoJwt alloc] init];
NSString *accessToken = [jsonToken StringOf: @"access_token"];
NSString *joseHeader = [jwt GetHeader: accessToken];

NSLog(@"%@",joseHeader);
// The joseHeader contains this:   {"kid":"anSaRDPfWGOSCVNZEIZB9quCbNsdsvl5uWGBzxbudWQ","alg":"RS256"}

CkoJsonObject *json = [[CkoJsonObject alloc] init];
[json Load: joseHeader];
NSString *kid = [json StringOf: @"kid"];
NSLog(@"%@%@",@"kid to find: ",kid);

// ------------------------
// Step 2: Find the key with the same "kid" in the Okta web keys.

CkoStringBuilder *sbKid = [[CkoStringBuilder alloc] init];
NSString *e = @"";
NSString *n = @"";

int i = 0;
int count_i = [[jsonWebKeys SizeOfArray: @"keys"] intValue];
BOOL bFound = NO;
int iMatch = 0;
while ((bFound == NO) && (i < count_i)) {
    jsonWebKeys.I = [NSNumber numberWithInt: i];
    [sbKid Clear];
    [jsonWebKeys StringOfSb: @"keys[i].kid" sb: sbKid];
    NSLog(@"%@%@",@"checking kid: ",[sbKid GetAsString]);

    if ([sbKid ContentsEqual: kid caseSensitive: YES] == YES) {
        e = [jsonWebKeys StringOf: @"keys[i].e"];
        n = [jsonWebKeys StringOf: @"keys[i].n"];
        // Exit the loop. 
        NSLog(@"%@",@"Found matching kid.");
        iMatch = i;
        bFound = YES;
    }

    i = i + 1;
}

if (bFound == NO) {
    NSLog(@"%@",@"No matching key ID found.");
    return;
}

NSLog(@"%@",@"Matching key:");
NSLog(@"%@%@",@"  exponent = ",e);
NSLog(@"%@%@",@"  modulus = ",n);

// ------------------------
// Step 3: Load the RSA modulus and exponent into a Chilkat public key object.
CkoPublicKey *pubkey = [[CkoPublicKey alloc] init];

// Get the matching JSON key from the array of keys.
jsonWebKeys.I = [NSNumber numberWithInt: iMatch];
CkoJsonObject *jsonWebKey = [jsonWebKeys ObjectOf: @"keys[i]"];
success = [pubkey LoadFromString: [jsonWebKey Emit]];
if (success == NO) {
    NSLog(@"%@",@"Failed to load JSON web key.");
    NSLog(@"%@",[jsonWebKey Emit]);
    NSLog(@"%@",pubkey.LastErrorText);

    return;
}

NSLog(@"%@",@"successfully loaded web key.");

// OK.. we have the desired JSON web key loaded into our public key object.
// Now we can verify the access token.

// ------------------------
// Step 4: Verify the access token.
BOOL bVerified = [jwt VerifyJwtPk: accessToken key: pubkey];
if (bVerified == YES) {
    NSLog(@"%@",@"The access token is valid.");
}
else {
    NSLog(@"%@",@"The access token is NOT valid.");
}