DataFlex

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>

DataFlex

Use ChilkatAx-win32.pkg

Procedure Test
    Boolean iSuccess
    Variant vPrivKey
    Handle hoPrivKey
    String sTokenEndpoint
    String sApiEndpoint
    Handle hoJson
    Handle hoHttp
    String sResp
    Integer iStatusCode
    String sTemp1
    Boolean bTemp1

    Move False To iSuccess

    Get Create (RefClass(cComChilkatPrivateKey)) To hoPrivKey
    If (Not(IsComObjectCreated(hoPrivKey))) Begin
        Send CreateComObject of hoPrivKey
    End

    // Load your ECDSA private key.  (Keys uses with DPoP must always be ECDSA keys.  Not RSA.)
    Get ComLoadAnyFormatFile Of hoPrivKey "qa_data/pem/ecc_privKey.pem" "" To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoPrivKey To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    Move "https://demo.duendesoftware.com/connect/token" To sTokenEndpoint
    Move "https://demo.duendesoftware.com/api/dpop/test" To sApiEndpoint

    // Provide the details needed for Chilkat to automatically fetch the access token
    // using the client_credentials OAuth2 flow.
    Get Create (RefClass(cComChilkatJsonObject)) To hoJson
    If (Not(IsComObjectCreated(hoJson))) Begin
        Send CreateComObject of hoJson
    End
    Get ComUpdateString Of hoJson "client_secret" "secret" To iSuccess
    Get ComUpdateString Of hoJson "client_id" "m2m.dpop" To iSuccess
    Get ComUpdateString Of hoJson "token_endpoint" sTokenEndpoint To iSuccess
    Get ComUpdateString Of hoJson "scope" "api" To iSuccess

    Get Create (RefClass(cComChilkatHttp)) To hoHttp
    If (Not(IsComObjectCreated(hoHttp))) Begin
        Send CreateComObject of hoHttp
    End
    Set ComSessionLogFilename Of hoHttp To "c:/aaworkarea/sessionLog.txt"

    // Provide private key to be used with DPoP
    Get pvComObject of hoPrivKey to vPrivKey
    Get ComSetDPoPKey Of hoHttp vPrivKey To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoHttp To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    Get ComEmit Of hoJson To sTemp1
    Set ComAuthToken Of hoHttp To sTemp1

    // 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.

    Get ComQuickGetStr Of hoHttp sApiEndpoint To sResp
    Get ComLastMethodSuccess Of hoHttp To bTemp1
    If (bTemp1 = False) Begin
        Get ComLastErrorText Of hoHttp To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    Get ComLastStatus Of hoHttp To iStatusCode

    Showln "response status code = " iStatusCode
    Showln sResp

    // 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
    // 
    // 


End_Procedure