(Objective-C) JWS Using HMAC SHA-256

Creates a JSON Web Signatures (JWS) using HMAC SHA-256.

Note: This example requires Chilkat v9.5.0.66 or greater.

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#import <CkoJsonObject.h>
#import <CkoJws.h>
#import <NSString.h>

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

// Note: This example requires Chilkat v9.5.0.66 or greater.

BOOL success;

// First create the JWS Protected Header
CkoJsonObject *jwsProtHdr = [[CkoJsonObject alloc] init];
[jwsProtHdr AppendString: @"typ" value: @"JWT"];
[jwsProtHdr AppendString: @"alg" value: @"HS256"];
NSLog(@"%@%@",@"JWS Protected Header: ",[jwsProtHdr Emit]);

// Output:
// JWS Protected Header: {"typ":"JWT","alg":"HS256"}

CkoJws *jws = [[CkoJws alloc] init];

// Set the HMAC key:
NSString *hmacKey = @"AyM1SysPpbyDfgZld3umj1qzKObwVMkoqQ-EstJQLr_T-1qS0gZH75aKtMN3Yj0iPS4hcgUuTwjAzZr1Z9CAow";
int signatureIndex = 0;
[jws SetMacKey: [NSNumber numberWithInt: signatureIndex] key: hmacKey encoding: @"base64url"];

// Set the protected header:
[jws SetProtectedHeader: [NSNumber numberWithInt: signatureIndex] json: jwsProtHdr];

// Set the payload.
BOOL bIncludeBom = NO;
NSString *payloadStr = @"In our village, folks say God crumbles up the old moon into stars.";
[jws SetPayload: payloadStr charset: @"utf-8" includeBom: bIncludeBom];

// Create the JWS
// By default, the compact serialization is used.
NSString *jwsCompact = [jws CreateJws];
if (jws.LastMethodSuccess != YES) {
    NSLog(@"%@",jws.LastErrorText);
    return;
}

NSLog(@"%@%@",@"JWS: ",jwsCompact);

// sample output:
// JWS: eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.SW4gb3VyIHZpbGxhZ2UsIGZvbGtzIHNheSBHb2QgY3J1bWJsZXMgdXAgdGhlIG9sZCBtb29uIGludG8gc3RhcnMu.bsYsi8HJ0N6OqGI1hKQ9QQRNPxxA5qMpcHLtOvXatk8

// Now load the JWS, validate, and recover the original text.
CkoJws *jws2 = [[CkoJws alloc] init];

// Load the JWS.
success = [jws2 LoadJws: jwsCompact];

// Set the MAC key used for validation.
signatureIndex = 0;
[jws2 SetMacKey: [NSNumber numberWithInt: signatureIndex] key: hmacKey encoding: @"base64url"];

// Validate the 1st (and only) signature at index 0..
int v = [[jws2 Validate: [NSNumber numberWithInt: signatureIndex]] intValue];
if (v < 0) {
    // Perhaps Chilkat was not unlocked or the trial expired..
    NSLog(@"%@",@"Method call failed for some other reason.");
    NSLog(@"%@",jws2.LastErrorText);
    return;
}

if (v == 0) {
    NSLog(@"%@",@"Invalid signature.  The MAC key was incorrect, the JWS was invalid, or both.");
    return;
}

// If we get here, the signature was validated..
NSLog(@"%@",@"Signature validated.");

// Recover the original content:
NSLog(@"%@",[jws2 GetPayload: @"utf-8"]);

// Examine the protected header:
CkoJsonObject *joseHeader = [jws2 GetProtectedHeader: [NSNumber numberWithInt: signatureIndex]];
if (jws2.LastMethodSuccess != YES) {
    NSLog(@"%@",@"No protected header found at the given index.");
    return;
}

joseHeader.EmitCompact = NO;

NSLog(@"%@",@"Protected (JOSE) header:");
NSLog(@"%@",[joseHeader Emit]);

// Output:

// 	Signature validated.
// 	In our village, folks say God crumbles up the old moon into stars.
// 	Protected (JOSE) header:
// 	{ 
// 	  "typ": "JWT",
// 	  "alg": "HS256"
// 	}