import base64


def sasl_plain_blob(username: str, passphrase: str) -> str:
    blob = base64.b64encode(
        b"\x00".join(
            (
                username.encode("utf-8"),
                username.encode("utf-8"),
                passphrase.encode("utf-8"),
            )
        )
    )
    blobstr = blob.decode("ascii")
    return f"AUTHENTICATE {blobstr}"