bitcoinlib signing raw text message using python

I am trying to sign a raw message, like "Hello World", using the Python library bitcoinlib. The goal is to generate a base64-encoded signature for the message that can be verified. However, bitcoinlib does not seem to offer a straightforward way to sign messages directly.

Here’s what I tried:

Using bitcoinlib.keys.Key: I attempted to use the key object for signing, but it doesn't directly support signing arbitrary messages. Using bitcoinlib.transactions.Transaction: This class is designed for signing Bitcoin transactions, but it doesn't support signing raw messages.

Issues:

Transaction.inputs_add() is not a valid method. Transaction.sign() does not accept message as an argument. It seems bitcoinlib is primarily designed for handling transactions, not arbitrary messages. Expected Behavior: I want to sign raw messages like "Hello World" and get a valid base64-encoded signature using bitcoinlib. Is there a better approach to achieve this with bitcoinlib, or do I need a different library?

Additional Info:

Python version: 3.11 bitcoinlib version: 0.6.0

from bitcoinlib.keys import Key
from bitcoinlib.transactions import Transaction

class BitcoinClient:
    def __init__(self, private_key_wif: str) -> None:
        """
        Initialize the BitcoinClient with a WIF private key.

        :param private_key_wif: The private key in Wallet Import Format (WIF).
        """
        self.key = Key(import_key=private_key_wif)
        self.address = self.key.address()

    def get_address(self) -> str:
        """
        Get the Bitcoin address associated with the private key.

        :return: Bitcoin address as a string.
        """
        return self.address

    def sign_message(self, message: str) -> str:
        """
        Sign a message using the private key.

        :param message: The message to be signed.
        :return: The signature as a base64-encoded string.
        """
        tx = Transaction(network=self.key.network)
        tx.inputs_add(self.key.address())
        signature = tx.sign(self.key, message=message)
        return signature

    def verify_message(self, message: str, signature: str) -> bool:
        """
        Verify a signed message.

        :param message: The original message.
        :param signature: The base64-encoded signature to verify.
        :return: True if the signature is valid, False otherwise.
        """
        tx = Transaction(network=self.key.network)
        return tx.verify_message(self.key.address(), message=message, signature=signature)

if __name__ == "__main__":
    # Expected address and signature for testing
    address_from_priv = ''
    # Signed message type which i should see
    signed = 'AUCozKGE8DkRwCIKgJdzwIY6nQ4lYkUlFnQqry5sDaKa9rHrpIUoIyD9I+nkRA0tCf1nwlfCeqUmMl6aSDBaLwn6'

    # Your WIF private key and message
    private_key_wif = ""
    message = "Hello world!"

    # Initialize the BitcoinClient
    try:
        signer = BitcoinClient(private_key_wif)

        # Sign the message
        signature = signer.sign_message(message)

        # Get the Bitcoin address
        address = signer.get_address()

        # Verify the signature
        is_valid = signer.verify_message(message, signature)

        # Output the results
        print(f"Bitcoin Address: {address}")
        print(f"Signature: {signature}")
        print(f"Is signature valid: {is_valid}")
        print(f"Is signature matching expected: {signature == signed}")
        print(f"Is address matching expected: {address == address_from_priv}")
    except ValueError as e:
        print(f"Error: {e}")