B4J Code Snippet Create JWT tokens and verify them

hello everyone i was in need to create jwt tokens and verify them in my b4j server app so i created this class. it comes to my mind to share it
it may be valuable to other fellow b4x member to achieve same goal.

Required libraries

Base64 and Encryption library by @agraham ​

JSON Library by @Erel

jStringutils library

here is the code snippet.

Sub Process_Globals
    Dim SECRET_KEY As String = "YourSecretkey123456" ' Your secret key - KEEP THIS SECRET!  Never expose it in client-side code.
    Dim ALGORITHM As String = "HMACSHA256" ' The hashing algorithm used for the signature.
End Sub

' Creates a JWT (JSON Web Token) for a given username.
Sub CreateJWT(username As String) As String
    Dim header As Map  ' JWT header (contains algorithm and token type).
    header.Initialize
    header.Put("alg", "HS256") ' Algorithm used for signing (HMAC-SHA256).
    header.Put("typ", "JWT") ' Type of token (JWT).

    Dim payload As Map ' JWT payload (contains user information and other claims).
    payload.Initialize
    payload.Put("sub", username) ' Subject (usually the username).
    payload.Put("iat", DateTime.Now) ' Issued at (timestamp when the token was created).
    payload.Put("exp", DateTime.Now + (1000 * 60 * 60)) ' Expires in 1 hour (timestamp when the token expires).

    Dim headerBase64 As String = B64_Encode(JsonStringify(header)) ' Base64 encode the header.
    Dim payloadBase64 As String = B64_Encode(JsonStringify(payload)) ' Base64 encode the payload.
    Dim signature As String = HMAC_SHA256(headerBase64 & "." & payloadBase64, SECRET_KEY) ' Calculate the signature.

    Return headerBase64 & "." & payloadBase64 & "." & signature ' Return the complete JWT (header.payload.signature).
End Sub

' Verifies a JWT.
Sub VerifyJWT(token As String) As Boolean
    Try
        Dim parts() As String = Regex.Split("\.", token) ' Split the token into its three parts.
        If parts.Length <> 3 Then ' Check if the token has the correct format.
            Log("Invalid token format")
            Return False
        End If

        Dim headerBase64 As String = parts(0) ' Extract the header.
        Dim payloadBase64 As String = parts(1) ' Extract the payload.
        Dim signatureReceived As String = parts(2) ' Extract the received signature.

        Dim signatureCalculated As String = HMAC_SHA256(headerBase64 & "." & payloadBase64, SECRET_KEY) ' Calculate the expected signature.

        If signatureCalculated <> signatureReceived Then ' Compare the calculated signature with the received signature.
            Log("Signature mismatch")
            Return False
        End If

        ' Optionally verify expiry
        Dim payloadJson As String = B64_Decode(payloadBase64) ' Decode the payload from Base64 to JSON.
        Dim parser As JSONParser
        parser.Initialize(payloadJson)
        Dim payloadMap As Map = parser.NextObject ' Parse the JSON payload.

        If payloadMap.ContainsKey("exp") Then ' Check if the payload contains an expiry time.
            Dim expiryTime As Long = payloadMap.Get("exp") ' Get the expiry time.
            If DateTime.Now > expiryTime Then ' Check if the token has expired.
                Log("Token expired")
                Return False
            End If
        End If

        Log("Token is valid") ' Token is valid.
        Return True

    Catch ' Handle any errors during verification.
        Log("Error verifying token: " & LastException.Message)
        Return False
    End Try
End Sub

' Converts a Map to a JSON string.
Sub JsonStringify(map As Map) As String
    Dim j As JSONGenerator
    Dim json As String
    j.Initialize(map)
    json = j.ToString
    Return json
End Sub

' Decodes a Base64 encoded string to a UTF8 string.
Sub B64_Decode(text As String) As String
    Dim Base64 As StringUtils
    Try
        Dim jsondataBytes() As Byte ' Store decoded bytes
        jsondataBytes = Base64.DecodeBase64(text) ' Decode Base64 to bytes
        Return BytesToString(jsondataBytes, 0, jsondataBytes.Length, "UTF8") ' Convert bytes to UTF8 string
    Catch ' Handle Base64 decoding errors.
        Log("Base64 Decode Error: " & LastException.Message)
        Return "" ' Or handle the error as needed
    End Try
End Sub

' Encodes a string to Base64 using UTF8 encoding.
Sub B64_Encode(text As String) As String
    Dim Base64 As StringUtils
    Return Base64.EncodeBase64(text.GetBytes("UTF8")) ' Encode the string to Base64 using UTF8.
End Sub

' Calculates the HMAC-SHA256 signature.
Sub HMAC_SHA256(data As String, key As String) As String
    Dim hmac As Mac
    Dim KG As KeyGenerator

    KG.Initialize(ALGORITHM) ' Initialize the KeyGenerator with the algorithm.
    KG.KeyFromBytes(key.GetBytes("UTF8")) ' Create a key from the secret key using UTF8 encoding.

    hmac.Initialise(ALGORITHM, KG.Key) ' Initialize the Mac object with the algorithm and key.
    hmac.Update(data.GetBytes("UTF8")) ' Update the Mac object with the data to be signed (using UTF8 encoding).
    Dim Base64 As StringUtils
    Return Base64.EncodeBase64(hmac.Sign) ' Calculate the signature and encode it to Base64.
End Sub