(Swift 3,4,5...) Verify Okta ID Token Locally

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

For more information, see https://developer.okta.com/docs/guides/validate-id-tokens/overview/

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func chilkatTest() {
    // 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 + id 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
    // 
    // 

    // ----------------------------------------------------------------
    // Note: The very last step of this example is where the claims, such as iss, aud, iat, exp, and nonce
    // are extracted from the ID token and examined.
    // ----------------------------------------------------------------

    // Load the access/id 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 id_token.  (The access_token is verified in this example:  Verify Okta Access Token

    let jsonToken = CkoJsonObject()!
    var success: Bool = 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"
    //     },
    //     {
    // 	...
    //     }
    //   ]
    // }

    let jsonWebKeys = CkoJsonObject()!
    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.
    // 
    let jwt = CkoJwt()!
    var idToken: String? = jsonToken.string(of: "id_token")
    var joseHeader: String? = jwt.getHeader(idToken)

    print("\(joseHeader!)")
    // The joseHeader contains this:   {"kid":"anSaRDPfWGOSCVNZEIZB9quCbNsdsvl5uWGBzxbudWQ","alg":"RS256"}

    let json = CkoJsonObject()!
    json.load(joseHeader)
    var kid: String? = json.string(of: "kid")
    print("kid to find: \(kid!)")

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

    let sbKid = CkoStringBuilder()!
    var e: String? = ""
    var n: String? = ""

    var i: Int = 0
    var count_i: Int = jsonWebKeys.size(ofArray: "keys").intValue
    var bFound: Bool = false
    var iMatch: Int = 0
    while (bFound == false) && (i < count_i) {
        jsonWebKeys.i = i
        sbKid.clear()
        jsonWebKeys.string(ofSb: "keys[i].kid", sb: sbKid)
        print("checking kid: \(sbKid.getAsString()!)")

        if sbKid.contentsEqual(kid, caseSensitive: true) == true {
            e = jsonWebKeys.string(of: "keys[i].e")
            n = jsonWebKeys.string(of: "keys[i].n")
            // Exit the loop. 
            print("Found matching kid.")
            iMatch = i
            bFound = true
        }

        i = i + 1
    }

    if bFound == false {
        print("No matching key ID found.")
        return
    }

    print("Matching key:")
    print("  exponent = \(e!)")
    print("  modulus = \(n!)")

    // ------------------------
    // Step 3: Load the RSA modulus and exponent into a Chilkat public key object.
    let pubkey = CkoPublicKey()!

    // Get the matching JSON key from the array of keys.
    jsonWebKeys.i = iMatch
    var jsonWebKey: CkoJsonObject? = jsonWebKeys.object(of: "keys[i]")
    success = pubkey.load(from: jsonWebKey!.emit())
    if success == false {
        print("Failed to load JSON web key.")
        print("\(jsonWebKey!.emit()!)")
        print("\(pubkey.lastErrorText!)")
        jsonWebKey = nil
        return
    }

    jsonWebKey = nil
    print("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.
    var bVerified: Bool = jwt.verifyJwtPk(idToken, key: pubkey)
    if bVerified == true {
        print("The ID token is valid.")
    }
    else {
        print("The ID token is NOT valid.")
    }

    // ------------------------
    // Step 5: Extract the claims (payload) from the ID token and examine them..

    var claims: String? = jwt.getPayload(idToken)

    let jsonClaims = CkoJsonObject()!
    jsonClaims.load(claims)
    jsonClaims.emitCompact = false
    print("\(jsonClaims.emit()!)")

    // Sample claims:
    // {
    //   "sub": "00utrr8ehubooPhjj356",
    //   "ver": 1,
    //   "iss": "https://dev-765951.okta.com/oauth2/default",
    //   "aud": "0oatrr20vPYgVDlGr356",
    //   "iat": 1562190727,
    //   "exp": 1562194327,
    //   "jti": "ID.JvlMhlnCj5ZqqGjk-jlgcOxHEyVUwIl9_Kpz69U2D_4",
    //   "amr": [
    //     "pwd"
    //   ],
    //   "idp": "00os29azljkqyx99Q356",
    //   "auth_time": 1562190726,
    //   "at_hash": "SLMiVeyNWWEDaZ-O32nKMg"
    // }

    // The exp (expiry time) claim is the time at which this token will expire., expressed in Unix time. You should make sure that this time has not already passed.
    let dtExp = CkoDateTime()!
    dtExp.setFromUnixTime(false, t: jsonClaims.int(of: "exp").intValue)
    print("expire timestamp = \(dtExp.getAsTimestamp(false)!)")

    // Check to see if this date/time expires within 0 seconds (i.e. is already past)
    var bExpired: Bool = dtExp.expires(within: 0, units: "seconds")
    print("bExpired = \(bExpired)")

}