(Visual FoxPro) Implementing DPoP with OAuth2 Client Credentials

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Demonstrating Proof-of-Possession (DPoP) is an OAuth 2.0 extension (RFC 9449) that secures access tokens by binding them to a specific client’s private key, preventing stolen token misuse. It requires the client to sign a JWT (DPoP Proof) with every request, proving they hold the private key.

This example shows how to use Chilkat v11.4.0 or later to automatically add the following headers to HTTP requests:

Authorization: DPoP <access_token>
DPoP: <new JWT signed with same key>

Note: This example requires Chilkat v11.4.0 or greater.

Chilkat ActiveX Downloads

ActiveX for 32-bit and 64-bit Windows

LOCAL lnSuccess
LOCAL loPrivKey
LOCAL lcTokenEndpoint
LOCAL lcApiEndpoint
LOCAL loJson
LOCAL loHttp
LOCAL lcResp
LOCAL lnStatusCode

lnSuccess = 0

loPrivKey = CreateObject('Chilkat.PrivateKey')

* Load your ECDSA private key.  (Keys uses with DPoP must always be ECDSA keys.  Not RSA.)
lnSuccess = loPrivKey.LoadAnyFormatFile("qa_data/pem/ecc_privKey.pem","")
IF (lnSuccess = 0) THEN
    ? loPrivKey.LastErrorText
    RELEASE loPrivKey
    CANCEL
ENDIF

lcTokenEndpoint = "https://demo.duendesoftware.com/connect/token"
lcApiEndpoint = "https://demo.duendesoftware.com/api/dpop/test"

* Provide the details needed for Chilkat to automatically fetch the access token
* using the client_credentials OAuth2 flow.
loJson = CreateObject('Chilkat.JsonObject')
loJson.UpdateString("client_secret","secret")
loJson.UpdateString("client_id","m2m.dpop")
loJson.UpdateString("token_endpoint",lcTokenEndpoint)
loJson.UpdateString("scope","api")

loHttp = CreateObject('Chilkat.Http')
loHttp.SessionLogFilename = "c:/aaworkarea/sessionLog.txt"

* Provide private key to be used with DPoP
lnSuccess = loHttp.SetDPoPKey(loPrivKey)
IF (lnSuccess = 0) THEN
    ? loHttp.LastErrorText
    RELEASE loPrivKey
    RELEASE loJson
    RELEASE loHttp
    CANCEL
ENDIF

loHttp.AuthToken = loJson.Emit()

* When we make the first request to an API endpoint, we don't yet have
* an OAuth2 access token.  Chilkat (internally) will use the token endpoint
* to automatically get an access token.
* Chilkat will then add the following headers to the request sent to the API endpoint:

* Authorization: DPoP <access_token>
* DPoP: <new JWT signed with same key>

* For subsequent requests using the same Chilkat HTTP object instance,
* the same access token will be used with a newly generated DPoP header for each request.
* When the access_token is expired or about to expire, Chilkat will automatically (internally)
* refresh the access token.  Your application does not need to be concerned with the 
* complexities of fetching the access token or managing the refresh, or generating
* the DPoP header for each request.

lcResp = loHttp.QuickGetStr(lcApiEndpoint)
IF (loHttp.LastMethodSuccess = 0) THEN
    ? loHttp.LastErrorText
    RELEASE loPrivKey
    RELEASE loJson
    RELEASE loHttp
    CANCEL
ENDIF

lnStatusCode = loHttp.LastStatus

? "response status code = " + STR(lnStatusCode)
? lcResp

* Here is a Session log showing the raw HTTP request(s) and response(s).
* Notice how Chilkat automatically fetched the access_token and then used it in the API request.

* ---- Sending Mon, 30 Mar 2026 20:09:44 GMT ----
* POST /connect/token HTTP/1.1
* Host: demo.duendesoftware.com
* Content-Type: application/x-www-form-urlencoded
* Content-Length: 79
* DPoP: ****
* 
* client_secret=secret&client_id=m2m.dpop&scope=api&grant_type=client_credentials
* ---- Received Mon, 30 Mar 2026 20:09:44 GMT ----
* HTTP/1.1 200 OK
* Date: Mon, 30 Mar 2026 20:09:43 GMT
* Content-Type: application/json; charset=UTF-8
* Transfer-Encoding: chunked
* Connection: keep-alive
* Server: Kestrel
* Cache-Control: no-store, no-cache, max-age=0
* Pragma: no-cache
* X-REVISION: 4f42f7e7
* 
* 374
* {"access_token":"eyJhbGciOiJSUzI1NiIsImtpZCI6IjE1OEUyRDQ1NzhFNDMyOUJBMzRGNzkxQTQ4Nzk5NzYwIiwieDV0IjoiczkyM2RnYnhWbnhoaTJSZmR1cWZyZXZIYUUwIi
* widHlwIjoiYXQrand0In0.eyJpc3MiOiJodHRwczovL2RlbW8uZHVlbmRlc29mdHdhcmUuY29tIiwibmJmIjoxNzc0OTAxMzgzLCJpYXQiOjE3NzQ5MDEzODMsImV4cCI6MTc3NDkwN
* Dk4MywiYXVkIjoiYXBpIiwiY25mIjp7ImprdCI6IlVMR2J4ZXdNOEZUNDhTd3hKeUY3YnJuMDZWMDdPZ3VpdW41d1ZzSVVENEUifSwic2NvcGUiOlsiYXBpIl0sImNsaWVudF9pZCI6
* Im0ybS5kcG9wIiwianRpIjoiQ0Q5MjBFQzQyOTRBOTA3QUUyRjMyQjlCREQzQTA3QzMifQ.bbq8tNMVtJp79Wc9xrAsE0h8oOfdxEKtGZ3qHpJX-mvSS4FVXLoO2bfpq1nhFryfbZkk
* ENfoIwSQjb_35aziq2NrnpWwQ4vDF1b9K-b7eJXPmJybm61DAP9HSE3ZI0jMrMTRFLtjwvE4WV6ZXNTwN0Pzn6teog1i09PZQkaGtlJEBjsBaN5N7OsQvtgFLD0sNkjy1JTw5LMNE7u
* 5-W32qv-XDk9KEGfoBkqyt-SR_A2wI7oZvl4OGnYyX8tUOFszlHZKy0_0V3Oc9wkHRM2JZDA_LfTqldJHR5CF5FuNiJ2hp-kioUA-i0gWxhqnVKVspJqQAN3Z95RDl9jSf-pYSg",
* "expires_in":3600,"token_type":"DPoP","scope":"api"}
* 0
* 
* 
* ---- Sending Mon, 30 Mar 2026 20:09:44 GMT ----
* GET /api/dpop/test HTTP/1.1
* Host: demo.duendesoftware.com
* Accept: */*
* Accept-Encoding: gzip
* Authorization: ****
* DPoP: ****
* 
* 
* ---- Received Mon, 30 Mar 2026 20:09:44 GMT ----
* HTTP/1.1 200 OK
* Date: Mon, 30 Mar 2026 20:09:44 GMT
* Content-Type: application/json; charset=utf-8
* Transfer-Encoding: chunked
* Connection: keep-alive
* Server: Kestrel
* X-REVISION: 4f42f7e7
* 
* 420
* [{"type":"iss","value":"https://demo.duendesoftware.com"},{"type":"nbf","value":"1774901383"},{"type":"iat","value":"1774901383"},
* {"type":"exp","value":"1774904983"},{"type":"aud","value":"api"},{"type":"cnf","value":"{\u0022jkt\u0022:\u0022ULGbxewM8FT48SwxJyF7brn06V07Oguiun5wVsIUD4E\u0022}"},
* {"type":"scope","value":"api"},{"type":"client_id","value":"m2m.dpop"},{"type":"jti","value":"CD920EC4294A907AE2F32B9BDD3A07C3"},
* {"type":"authorization_scheme","value":"DPoP"},{"type":"proof_token","value":"eyJhbGciOiJFU .... aGrGOgkRXLQ"}]
* 0
* 
* 

RELEASE loPrivKey
RELEASE loJson
RELEASE loHttp