How to use the fastecdsa.encoding.pem.PEMEncoder.decode_public_key function in fastecdsa

If the signature is valid, returns True. If the signature is invalid, raise
    an exception explaining why.
    """
    # Data must be encoded as bytes
    if isinstance(data, str):
        data = data.encode()

    # Content signature implicitly adds a prefix to signed data
    data = b"Content-Signature:\x00" + data

    # fastecdsa expects ASCII armored keys, but ours is unarmored. Add the
    # armor before passing the key to the library.
    EC_PUBLIC_HEADER = "-----BEGIN PUBLIC KEY-----"
    EC_PUBLIC_FOOTER = "-----END PUBLIC KEY-----"
    verifying_pubkey = PEMEncoder.decode_public_key(
        "\n".join([EC_PUBLIC_HEADER, pubkey, EC_PUBLIC_FOOTER])
    )

    try:
        signature = base64.urlsafe_b64decode(signature)
        signature = ecdsa.util.sigdecode_string(signature, order=ecdsa.curves.NIST384p.order)
    except binascii.Error as e:
        if BASE64_WRONG_LENGTH_RE.match(e.args[0]):
            raise WrongSignatureSize("Base64 encoded signature was not a multiple of 4")
        else:
            raise
    except AssertionError as e:
        # The signature decoder has a clause like
        #     assert len(signature) == 2*l, (len(signature), 2*l)
        # If the AssertionError is consistent with that signature, translate it
        # to a nicer error. Otherwise re-raise.