(PureBasic) Verify JWT Using HS256, HS384, or HS512

Demonstrates how to verify a JWT that was signed using HS256, HS384, or HS512. (HS256 is JWT's acronym for HMAC-SHA256.)

This example verifies the signature. It also does the following:

• Checks to see if the time constraints ("nbf" and "exp") are valid.
• Recovers the original JOSE header.
• Recovers the original claims JSON.

Chilkat PureBasic Module Download Chilkat PureBasic Module

IncludeFile "CkJwt.pb"
IncludeFile "CkJsonObject.pb"

Procedure ChilkatExample()

    ; Demonstrates how to verify an HMAC JWT using a shared secret (password).

    ; This example requires the Chilkat API to have been previously unlocked.
    ; See Global Unlock Sample for sample code.

    jwt.i = CkJwt::ckCreate()
    If jwt.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    token.s = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJodHRwOi8vZXhhbXBsZS5vcmciLCJzdWIiOiJKb2huIiwiYXVkIjoiaHR0cDovL2V4YW1wbGUuY29tIiwiaWF0IjoxNDYzNDMxODEyLCJuYmYiOjE0NjM0MzE4MTIsImV4cCI6MTQ2MzQzNTQxMn0.SHnMJ11qJH5pbp22YchT_9fL2HIx0koHiUHLG67_foU"

    ; First verify the signature.
    ; The password used to create this JWT was "secret".
    sigVerified.i = CkJwt::ckVerifyJwt(jwt,token,"secret")
    Debug "with correct password: " + Str(sigVerified)

    ; Now try with a different password:
    sigVerified = CkJwt::ckVerifyJwt(jwt,token,"secret2")
    Debug "with incorrect password " + Str(sigVerified)

    ; Let's see if the time constraints, if any, are valid.
    ; The above JWT was created on the afternoon of 16-May-2016, with an expiration of 1 hour.
    ; If the current system time is before the "nbf" time, or after the "exp" time,
    ; then IsTimeValid will return false/0.
    ; Also, we'll allow a leeway of 60 seconds to account for any clock skew.
    ; Note: If the token has no "nbf" or "exp" claim fields, then IsTimeValid is always true.
    leeway.i = 60
    bTimeValid.i = CkJwt::ckIsTimeValid(jwt,token,leeway)
    Debug "time constraints valid: " + Str(bTimeValid)

    ; Now let's recover the original claims JSON (the payload).
    payload.s = CkJwt::ckGetPayload(jwt,token)
    ; The payload will likely be in compact form:
    Debug payload

    ; We can format for human viewing by loading it into Chilkat's JSON object
    ; and emit.
    json.i = CkJsonObject::ckCreate()
    If json.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success.i = CkJsonObject::ckLoad(json,payload)
    CkJsonObject::setCkEmitCompact(json, 0)
    Debug CkJsonObject::ckEmit(json)

    ; We can recover the original JOSE header in the same way:
    joseHeader.s = CkJwt::ckGetHeader(jwt,token)
    ; The payload will likely be in compact form:
    Debug joseHeader

    ; We can format for human viewing by loading it into Chilkat's JSON object
    ; and emit.
    success = CkJsonObject::ckLoad(json,joseHeader)
    CkJsonObject::setCkEmitCompact(json, 0)
    Debug CkJsonObject::ckEmit(json)


    CkJwt::ckDispose(jwt)
    CkJsonObject::ckDispose(json)


    ProcedureReturn
EndProcedure