(Objective-C) Verify JWT Using HS256, HS384, or HS512

Demonstrates how to verify a JWT that was signed using HS256, HS384, or HS512. (HS256 is JWT's acronym for HMAC-SHA256.)

This example verifies the signature. It also does the following:

• Checks to see if the time constraints ("nbf" and "exp") are valid.
• Recovers the original JOSE header.
• Recovers the original claims JSON.

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

// Demonstrates how to verify an HMAC JWT using a shared secret (password).

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

CkoJwt *jwt = [[CkoJwt alloc] init];

NSString *token = @"eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJodHRwOi8vZXhhbXBsZS5vcmciLCJzdWIiOiJKb2huIiwiYXVkIjoiaHR0cDovL2V4YW1wbGUuY29tIiwiaWF0IjoxNDYzNDMxODEyLCJuYmYiOjE0NjM0MzE4MTIsImV4cCI6MTQ2MzQzNTQxMn0.SHnMJ11qJH5pbp22YchT_9fL2HIx0koHiUHLG67_foU";

// First verify the signature.
// The password used to create this JWT was "secret".
BOOL sigVerified = [jwt VerifyJwt: token password: @"secret"];
NSLog(@"%@%d",@"with correct password: ",sigVerified);

// Now try with a different password:
sigVerified = [jwt VerifyJwt: token password: @"secret2"];
NSLog(@"%@%d",@"with incorrect password ",sigVerified);

// Let's see if the time constraints, if any, are valid.
// The above JWT was created on the afternoon of 16-May-2016, with an expiration of 1 hour.
// If the current system time is before the "nbf" time, or after the "exp" time,
// then IsTimeValid will return false/0.
// Also, we'll allow a leeway of 60 seconds to account for any clock skew.
// Note: If the token has no "nbf" or "exp" claim fields, then IsTimeValid is always true.
int leeway = 60;
BOOL bTimeValid = [jwt IsTimeValid: token leeway: [NSNumber numberWithInt: leeway]];
NSLog(@"%@%d",@"time constraints valid: ",bTimeValid);

// Now let's recover the original claims JSON (the payload).
NSString *payload = [jwt GetPayload: token];
// The payload will likely be in compact form:
NSLog(@"%@",payload);

// We can format for human viewing by loading it into Chilkat's JSON object
// and emit.
CkoJsonObject *json = [[CkoJsonObject alloc] init];
BOOL success = [json Load: payload];
json.EmitCompact = NO;
NSLog(@"%@",[json Emit]);

// We can recover the original JOSE header in the same way:
NSString *joseHeader = [jwt GetHeader: token];
// The payload will likely be in compact form:
NSLog(@"%@",joseHeader);

// We can format for human viewing by loading it into Chilkat's JSON object
// and emit.
success = [json Load: joseHeader];
json.EmitCompact = NO;
NSLog(@"%@",[json Emit]);