(Visual FoxPro) Verify Okta Access Token Locally

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

For more information, see https://developer.okta.com/docs/guides/validate-access-tokens/overview/#what-to-check-when-validating-an-access-token

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LOCAL loJsonToken
LOCAL lnSuccess
LOCAL loJsonWebKeys
LOCAL loJwt
LOCAL lcAccessToken
LOCAL lcJoseHeader
LOCAL loJson
LOCAL lcKid
LOCAL loSbKid
LOCAL e
LOCAL n
LOCAL i
LOCAL lnCount_i
LOCAL lnBFound
LOCAL lnIMatch
LOCAL loPubkey
LOCAL loJsonWebKey
LOCAL lnBVerified

* 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 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
* 
* 

* Load the access 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 access_token.  (The id_token is verified in this example:  Verify Okta ID Token

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.JsonObject')
loJsonToken = CreateObject('Chilkat.JsonObject')
lnSuccess = loJsonToken.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"
*     },
*     {
* 	...
*     }
*   ]
* }

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.JsonObject')
loJsonWebKeys = CreateObject('Chilkat.JsonObject')
lnSuccess = loJsonWebKeys.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.
* 
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Jwt')
loJwt = CreateObject('Chilkat.Jwt')
lcAccessToken = loJsonToken.StringOf("access_token")
lcJoseHeader = loJwt.GetHeader(lcAccessToken)

? lcJoseHeader
* The joseHeader contains this:   {"kid":"anSaRDPfWGOSCVNZEIZB9quCbNsdsvl5uWGBzxbudWQ","alg":"RS256"}

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.JsonObject')
loJson = CreateObject('Chilkat.JsonObject')
loJson.Load(lcJoseHeader)
lcKid = loJson.StringOf("kid")
? "kid to find: " + lcKid

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

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.StringBuilder')
loSbKid = CreateObject('Chilkat.StringBuilder')
e = ""
n = ""

i = 0
lnCount_i = loJsonWebKeys.SizeOfArray("keys")
lnBFound = 0
lnIMatch = 0
DO WHILE (lnBFound = 0) AND (i < lnCount_i)
    loJsonWebKeys.I = i
    loSbKid.Clear()
    loJsonWebKeys.StringOfSb("keys[i].kid",loSbKid)
    ? "checking kid: " + loSbKid.GetAsString()

    IF (loSbKid.ContentsEqual(lcKid,1) = 1) THEN
        e = loJsonWebKeys.StringOf("keys[i].e")
        n = loJsonWebKeys.StringOf("keys[i].n")
        * Exit the loop. 
        ? "Found matching kid."
        lnIMatch = i
        lnBFound = 1
    ENDIF

    i = i + 1
ENDDO

IF (lnBFound = 0) THEN
    ? "No matching key ID found."
    RELEASE loJsonToken
    RELEASE loJsonWebKeys
    RELEASE loJwt
    RELEASE loJson
    RELEASE loSbKid
    CANCEL
ENDIF

? "Matching key:"
? "  exponent = " + e
? "  modulus = " + n

* ------------------------
* Step 3: Load the RSA modulus and exponent into a Chilkat public key object.
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.PublicKey')
loPubkey = CreateObject('Chilkat.PublicKey')

* Get the matching JSON key from the array of keys.
loJsonWebKeys.I = lnIMatch
loJsonWebKey = loJsonWebKeys.ObjectOf("keys[i]")
lnSuccess = loPubkey.LoadFromString(loJsonWebKey.Emit())
IF (lnSuccess = 0) THEN
    ? "Failed to load JSON web key."
    ? loJsonWebKey.Emit()
    ? loPubkey.LastErrorText
    RELEASE loJsonWebKey
    RELEASE loJsonToken
    RELEASE loJsonWebKeys
    RELEASE loJwt
    RELEASE loJson
    RELEASE loSbKid
    RELEASE loPubkey
    CANCEL
ENDIF

RELEASE loJsonWebKey
? "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.
lnBVerified = loJwt.VerifyJwtPk(lcAccessToken,loPubkey)
IF (lnBVerified = 1) THEN
    ? "The access token is valid."
ELSE
    ? "The access token is NOT valid."
ENDIF

RELEASE loJsonToken
RELEASE loJsonWebKeys
RELEASE loJwt
RELEASE loJson
RELEASE loSbKid
RELEASE loPubkey