(Classic ASP) 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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' 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")
set jsonToken = Server.CreateObject("Chilkat.JsonObject")
success = 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"
'     },
'     {
' 	...
'     }
'   ]
' }

' For versions of Chilkat < 10.0.0, use CreateObject("Chilkat_9_5_0.JsonObject")
set jsonWebKeys = Server.CreateObject("Chilkat.JsonObject")
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.
' 
' For versions of Chilkat < 10.0.0, use CreateObject("Chilkat_9_5_0.Jwt")
set jwt = Server.CreateObject("Chilkat.Jwt")
accessToken = jsonToken.StringOf("access_token")
joseHeader = jwt.GetHeader(accessToken)

Response.Write "<pre>" & Server.HTMLEncode( joseHeader) & "</pre>"
' The joseHeader contains this:   {"kid":"anSaRDPfWGOSCVNZEIZB9quCbNsdsvl5uWGBzxbudWQ","alg":"RS256"}

' For versions of Chilkat < 10.0.0, use CreateObject("Chilkat_9_5_0.JsonObject")
set json = Server.CreateObject("Chilkat.JsonObject")
success = json.Load(joseHeader)
kid = json.StringOf("kid")
Response.Write "<pre>" & Server.HTMLEncode( "kid to find: " & kid) & "</pre>"

' ------------------------
' 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")
set sbKid = Server.CreateObject("Chilkat.StringBuilder")
e = ""
n = ""

i = 0
count_i = jsonWebKeys.SizeOfArray("keys")
bFound = 0
iMatch = 0
Do While (bFound = 0) And (i < count_i)
    jsonWebKeys.I = i
    sbKid.Clear 
    success = jsonWebKeys.StringOfSb("keys[i].kid",sbKid)
    Response.Write "<pre>" & Server.HTMLEncode( "checking kid: " & sbKid.GetAsString()) & "</pre>"

    If (sbKid.ContentsEqual(kid,1) = 1) Then
        e = jsonWebKeys.StringOf("keys[i].e")
        n = jsonWebKeys.StringOf("keys[i].n")
        ' Exit the loop. 
        Response.Write "<pre>" & Server.HTMLEncode( "Found matching kid.") & "</pre>"
        iMatch = i
        bFound = 1
    End If

    i = i + 1
Loop

If (bFound = 0) Then
    Response.Write "<pre>" & Server.HTMLEncode( "No matching key ID found.") & "</pre>"
    Response.End
End If

Response.Write "<pre>" & Server.HTMLEncode( "Matching key:") & "</pre>"
Response.Write "<pre>" & Server.HTMLEncode( "  exponent = " & e) & "</pre>"
Response.Write "<pre>" & Server.HTMLEncode( "  modulus = " & n) & "</pre>"

' ------------------------
' 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")
set pubkey = Server.CreateObject("Chilkat.PublicKey")

' Get the matching JSON key from the array of keys.
jsonWebKeys.I = iMatch
' jsonWebKey is a Chilkat.JsonObject
Set jsonWebKey = jsonWebKeys.ObjectOf("keys[i]")
success = pubkey.LoadFromString(jsonWebKey.Emit())
If (success = 0) Then
    Response.Write "<pre>" & Server.HTMLEncode( "Failed to load JSON web key.") & "</pre>"
    Response.Write "<pre>" & Server.HTMLEncode( jsonWebKey.Emit()) & "</pre>"
    Response.Write "<pre>" & Server.HTMLEncode( pubkey.LastErrorText) & "</pre>"

    Response.End
End If

Response.Write "<pre>" & Server.HTMLEncode( "successfully loaded web key.") & "</pre>"

' 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.
bVerified = jwt.VerifyJwtPk(accessToken,pubkey)
If (bVerified = 1) Then
    Response.Write "<pre>" & Server.HTMLEncode( "The access token is valid.") & "</pre>"
Else
    Response.Write "<pre>" & Server.HTMLEncode( "The access token is NOT valid.") & "</pre>"
End If


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