(Swift 3,4,5...) Validate a Google ID Token

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

Chilkat Downloads for the Swift Programming Language MAC OS X (Cocoa) Objective-C/Swift Libs iOS Objective-C/Swift Libs

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

    let http = CkoHttp()!

    // First get the public key we'll be needing..
    var jwkStr: String? = http.quickGetStr("https://www.googleapis.com/oauth2/v3/certs")
    if http.lastMethodSuccess == false {
        print("\(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"
    // 	}
    //       ]
    //     }

    let json = CkoJsonObject()!
    var success: Bool = 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"
    // }

    let jsonToken = CkoJsonObject()!
    success = jsonToken.loadFile("qa_data/tokens/google_sample_id_token.json")
    if success == false {
        print("Failed to load the JSON file...")
        return
    }

    // Get the id_token;
    let sbIdToken = CkoStringBuilder()!
    success = sbIdToken.append(jsonToken.string(of: "id_token"))

    // Get the signature in base64url format.
    // The header + payload remains in sbIdToken.
    var sig_b64Url: String? = sbIdToken.getAfterFinal(".", removeFlag: true)
    var headerPlusPayload: String? = sbIdToken.getAsString()

    print("\(sig_b64Url!)")
    print("\(headerPlusPayload!)")

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

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

    let rsa = CkoRsa()!
    rsa.encodingMode = "base64url"

    var numKeys: Int = json.size(ofArray: "keys").intValue
    var i: Int = 0
    while i < numKeys {
        json.i = i
        var jsonKey: CkoJsonObject? = json.object(of: "keys[i]")
        let pubKey = CkoPublicKey()!
        success = pubKey.load(from: jsonKey!.emit())
        if success == false {
            print("\(pubKey.lastErrorText!)")
            return
        }

        print("\(i)")
        print("\(pubKey.getPem(true)!)")
        jsonKey = nil

        success = rsa.importPublicKeyObj(pubKey)

        var bVerified: Bool = rsa.verifyStringENC(headerPlusPayload, hashAlg: "sha256", sig: sig_b64Url)
        print("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

}