Objective-C

Validate a Google ID Token

See more OAuth2 Examples

Demonstrates how to verify the signature of a Google id token. Objective-C

#import <CkoHttp.h>
#import <NSString.h>
#import <CkoJsonObject.h>
#import <CkoStringBuilder.h>
#import <CkoRsa.h>
#import <CkoPublicKey.h>

BOOL success = NO;

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

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

//  First get the public key we'll be needing..
NSString *jwkStr = [http QuickGetStr: @"https://www.googleapis.com/oauth2/v3/certs"];
if (http.LastMethodSuccess == NO) {
    NSLog(@"%@",http.LastErrorText);
    return;
}

//  We have the following:

//      {
//        "keys": [
//  	{
//  	  "kid": "e8732db06287515556213b80acbcfd08cfb302a9",
//  	  "n": "4RIrO30287Wsq3gqXCMkUYMVAeI3H8...w2mbMNEBQ",
//  	  "kty": "RSA",
//  	  "e": "AQAB",
//  	  "alg": "RS256",
//  	  "use": "sig"
//  	},
//  	{
//  	  "kid": "8462a71da4f6d611fc0fecf0fc4ba9c37d65e6cd",
//  	  "e": "AQAB",
//  	  "n": "xT_ngLZNmT5GBtJZeTB...Ft4gK0eoFi0d3l8bcw",
//  	  "alg": "RS256",
//  	  "use": "sig",
//  	  "kty": "RSA"
//  	}
//        ]
//      }

CkoJsonObject *json = [[CkoJsonObject alloc] init];
success = [json Load: jwkStr];

//  -------------------------------------------------

//  Load the following..

//   {
//    "access_token": "ya29.a0...0f",
//    "expires_in": 3599,
//    "scope": "openid https://www.googleapis.com/auth/userinfo.email",
//    "token_type": "Bearer",
//    "id_token": "eyJhb...o5nQ"
//  }

CkoJsonObject *jsonToken = [[CkoJsonObject alloc] init];
success = [jsonToken LoadFile: @"qa_data/tokens/google_sample_id_token.json"];
if (success == NO) {
    NSLog(@"%@",@"Failed to load the JSON file...");
    return;
}

//  Get the id_token;
CkoStringBuilder *sbIdToken = [[CkoStringBuilder alloc] init];
success = [sbIdToken Append: [jsonToken StringOf: @"id_token"]];

//  Get the signature in base64url format.
//  The header + payload remains in sbIdToken.
NSString *sig_b64Url = [sbIdToken GetAfterFinal: @"." removeFlag: YES];
NSString *headerPlusPayload = [sbIdToken GetAsString];

NSLog(@"%@",sig_b64Url);
NSLog(@"%@",headerPlusPayload);

//  ---------------------------------------------

//  Try validating with each cert's public key.
//  Hopefully one will be the key that verifies.

CkoRsa *rsa = [[CkoRsa alloc] init];
rsa.EncodingMode = @"base64url";

CkoJsonObject *jsonKey = [[CkoJsonObject alloc] init];
CkoPublicKey *pubKey = [[CkoPublicKey alloc] init];

int numKeys = [[json SizeOfArray: @"keys"] intValue];
int i = 0;
while (i < numKeys) {
    json.I = [NSNumber numberWithInt: i];

    [json ObjectOf2: @"keys[i]" jsonObj: jsonKey];

    success = [pubKey LoadFromString: [jsonKey Emit]];
    if (success == NO) {
        NSLog(@"%@",pubKey.LastErrorText);
        return;
    }

    NSLog(@"%d",i);
    NSLog(@"%@",[pubKey GetPem: YES]);

    success = [rsa UsePublicKey: pubKey];

    BOOL bVerified = [rsa VerifyStringENC: headerPlusPayload hashAlg: @"sha256" sig: sig_b64Url];
    NSLog(@"%@%d",@"bVerified = ",bVerified);

    i = i + 1;
}

//  The output is:

//  0
//  -----BEGIN RSA PUBLIC KEY-----
//  MIIBCgKCAQEA4RIrO30287Wsq3gqXCMkUYMVAeI3H8LVE6IXR1krdFeGnZLiGUPw
//  cbkeVpXf3lmJdsStOg+jijces2DZCfPyIBiQuLYfxxmAZE6ErJ0QJFg1stwli2Pz
//  9ncYhFoqi8pXr7kEzEJBTzX4thuw56ydbGsshSEznPXoerCJOc7UI2+n0wFCWQ4Y
//  LHbh/PrWt4vdadyUUUW/QpQHXQLdD8q/Qwqdj0O9zlJE7R6Elw2E9EqnHyIGu1hm
//  LxhqrTru1M18SUhONYbVskV/BCEdVKs//X96849HorWQDCAgVMWfGsdMVq55FAdJ
//  680N5UmQDRynIZ4+PeNGN4S9iw2mbMNEBQIDAQAB
//  -----END RSA PUBLIC KEY-----
//  
//  bVerified = True
//  1
//  -----BEGIN RSA PUBLIC KEY-----
//  MIIBCgKCAQEAxT/ngLZNmT5GBdkLtJZjNeTB+8B5yWgrq/e5eMZ1hrZhcmLK+dSn
//  IkpOPV8/OekV67EnQ7I4II2rcNJnHGrGKZziXO3XN2gtUHE+mBJC99oULSbX/QwB
//  Kz7gC/IBPq9EuxTt6Oq6fPkVQ9DbRIgWJSEGBF/KRaNl3kyAlIZfpY7XgHyJTTv8
//  E7yAcYKPR+36gzdl+ps0sDLKzUuAtZNq8llK0u80z6AtAUIYwWdkEhM9upy6keKI
//  TasIxcsO7M6kZPINUSbh6t5VAm8FuqRmxpgg+9c9/GQSGd89InVypoVzWLQ+wOGg
//  5G4H6JqIgtj0TRFt4gK0eoFi2U0d3l8bcwIDAQAB
//  -----END RSA PUBLIC KEY-----
//  
//  bVerified = False