(VB.NET) Validate JWS Using HMAC SHA-256

Validates a JSON Web Signature (JWS) using HMAC SHA-256.

Note: This example requires Chilkat v9.5.0.66 or greater.

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

' Note: This example requires Chilkat v9.5.0.66 or greater.

' This example takes a JSON signature in compact serialization format,
' and uses a MAC key to validate and recover the protected header and payload.


Dim jws As New Chilkat.Jws

' Set the HMAC key:
Dim hmacKey As String = "AyM1SysPpbyDfgZld3umj1qzKObwVMkoqQ-EstJQLr_T-1qS0gZH75aKtMN3Yj0iPS4hcgUuTwjAzZr1Z9CAow"
Dim signatureIndex As Integer = 0
jws.SetMacKey(signatureIndex,hmacKey,"base64url")

' Load the JWS.
Dim jwsCompact As String = "eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9.eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ.dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk"
Dim success As Boolean = jws.LoadJws(jwsCompact)

' Validate the 1st (and only) signature at index 0..
Dim v As Integer = jws.Validate(signatureIndex)
If (v < 0) Then
    ' Perhaps Chilkat was not unlocked or the trial expired..
    Debug.WriteLine("Method call failed for some other reason.")
    Debug.WriteLine(jws.LastErrorText)
    Exit Sub
End If

If (v = 0) Then
    Debug.WriteLine("Invalid signature.  The MAC key was incorrect, the JWS was invalid, or both.")
    Exit Sub
End If


' If we get here, the signature was validated..
Debug.WriteLine("Signature validated.")

' Recover the original content:
Debug.WriteLine("Recovered content:")
Debug.WriteLine(jws.GetPayload("utf-8"))

' Examine the protected header:
Dim joseHeader As Chilkat.JsonObject = jws.GetProtectedHeader(signatureIndex)
If (jws.LastMethodSuccess <> True) Then
    Debug.WriteLine("No protected header found at the given index.")
    Exit Sub
End If

joseHeader.EmitCompact = False

Debug.WriteLine("Protected (JOSE) header:")
Debug.WriteLine(joseHeader.Emit())


' Output:

' 	Signature validated.
' 	Recovered content:
' 	{"iss":"joe",
' 	 "exp":1300819380,
' 	 "http://example.com/is_root":true}
' 	Protected (JOSE) header:
' 	{ 
' 	  "typ": "JWT",
' 	  "alg": "HS256"
' 	}