# Copyright (c) 2022, Oracle and/or its affiliates.
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License, version 2.0, as
# published by the Free Software Foundation.
#
# This program is also distributed with certain software (including
# but not limited to OpenSSL) that is licensed under separate terms,
# as designated in a particular file or component or in included license
# documentation.  The authors of MySQL hereby grant you an
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#
# Without limiting anything contained in the foregoing, this file,
# which is part of MySQL Connector/Python, is also subject to the
# Universal FOSS Exception, version 1.0, a copy of which can be found at
# http://oss.oracle.com/licenses/universal-foss-exception.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
# See the GNU General Public License, version 2.0, for more details.
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# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA

"""LDAP SASL Authentication Plugin."""

import hmac
import logging

from base64 import b64decode, b64encode
from hashlib import sha1, sha256
from uuid import uuid4

from .. import errors

try:
    import gssapi
except ImportError:
    raise errors.ProgrammingError(
        "Module gssapi is required for GSSAPI authentication "
        "mechanism but was not found. Unable to authenticate "
        "with the server"
    ) from None

from ..utils import (
    normalize_unicode_string as norm_ustr,
    validate_normalized_unicode_string as valid_norm,
)
from . import BaseAuthPlugin

logging.getLogger(__name__).addHandler(logging.NullHandler())

_LOGGER = logging.getLogger(__name__)

AUTHENTICATION_PLUGIN_CLASS = "MySQLLdapSaslPasswordAuthPlugin"


# pylint: disable=c-extension-no-member,no-member
class MySQLLdapSaslPasswordAuthPlugin(BaseAuthPlugin):
    """Class implementing the MySQL ldap sasl authentication plugin.

    The MySQL's ldap sasl authentication plugin support two authentication
    methods SCRAM-SHA-1 and GSSAPI (using Kerberos). This implementation only
    support SCRAM-SHA-1 and SCRAM-SHA-256.

    SCRAM-SHA-1 amd SCRAM-SHA-256
        This method requires 2 messages from client and 2 responses from
        server.

        The first message from client will be generated by prepare_password(),
        after receive the response from the server, it is required that this
        response is passed back to auth_continue() which will return the
        second message from the client. After send this second message to the
        server, the second server respond needs to be passed to auth_finalize()
        to finish the authentication process.
    """

    sasl_mechanisms = ["SCRAM-SHA-1", "SCRAM-SHA-256", "GSSAPI"]
    requires_ssl = False
    plugin_name = "authentication_ldap_sasl_client"
    def_digest_mode = sha1
    client_nonce = None
    client_salt = None
    server_salt = None
    krb_service_principal = None
    iterations = 0
    server_auth_var = None
    target_name = None
    ctx = None
    servers_first = None
    server_nonce = None

    @staticmethod
    def _xor(bytes1, bytes2):
        return bytes([b1 ^ b2 for b1, b2 in zip(bytes1, bytes2)])

    def _hmac(self, password, salt):
        digest_maker = hmac.new(password, salt, self.def_digest_mode)
        return digest_maker.digest()

    def _hi(self, password, salt, count):
        """Prepares Hi
        Hi(password, salt, iterations) where Hi(p,s,i) is defined as
        PBKDF2 (HMAC, p, s, i, output length of H).
        """
        pw = password.encode()
        hi = self._hmac(pw, salt + b"\x00\x00\x00\x01")
        aux = hi
        for _ in range(count - 1):
            aux = self._hmac(pw, aux)
            hi = self._xor(hi, aux)
        return hi

    @staticmethod
    def _normalize(string):
        norm_str = norm_ustr(string)
        broken_rule = valid_norm(norm_str)
        if broken_rule is not None:
            raise errors.InterfaceError(f"broken_rule: {broken_rule}")
        return norm_str

    def _first_message(self):
        """This method generates the first message to the server to start the

        The client-first message consists of a gs2-header,
        the desired username, and a randomly generated client nonce cnonce.

        The first message from the server has the form:
            b'n,a=<user_name>,n=<user_name>,r=<client_nonce>

        Returns client's first message
        """
        cfm_fprnat = "n,a={user_name},n={user_name},r={client_nonce}"
        self.client_nonce = str(uuid4()).replace("-", "")
        cfm = cfm_fprnat.format(
            user_name=self._normalize(self._username),
            client_nonce=self.client_nonce,
        )

        if isinstance(cfm, str):
            cfm = cfm.encode("utf8")
        return cfm

    def _first_message_krb(self):
        """Get a TGT Authentication request and initiates security context.

        This method will contact the Kerberos KDC in order of obtain a TGT.
        """
        _LOGGER.debug("# user name: %s", self._username)
        user_name = gssapi.raw.names.import_name(
            self._username.encode("utf8"), name_type=gssapi.NameType.user
        )

        # Use defaults store = {'ccache': 'FILE:/tmp/krb5cc_1000'}#,
        #                       'keytab':'/etc/some.keytab' }
        # Attempt to retrieve credential from default cache file.
        try:
            cred = gssapi.Credentials()
            _LOGGER.debug(
                "# Stored credentials found, if password was given it will be ignored."
            )
            try:
                # validate credentials has not expired.
                cred.lifetime
            except gssapi.raw.exceptions.ExpiredCredentialsError as err:
                _LOGGER.warning(" Credentials has expired: %s", err)
                cred.acquire(user_name)
                raise errors.InterfaceError(f"Credentials has expired: {err}")
        except gssapi.raw.misc.GSSError as err:
            if not self._password:
                raise errors.InterfaceError(
                    f"Unable to retrieve stored credentials error: {err}"
                )
            try:
                _LOGGER.debug("# Attempt to retrieve credentials with given password")
                acquire_cred_result = gssapi.raw.acquire_cred_with_password(
                    user_name,
                    self._password.encode("utf8"),
                    usage="initiate",
                )
                cred = acquire_cred_result[0]
            except gssapi.raw.misc.GSSError as err2:
                raise errors.ProgrammingError(
                    f"Unable to retrieve credentials with the given password: {err2}"
                )

        flags_l = (
            gssapi.RequirementFlag.mutual_authentication,
            gssapi.RequirementFlag.extended_error,
            gssapi.RequirementFlag.delegate_to_peer,
        )

        if self.krb_service_principal:
            service_principal = self.krb_service_principal
        else:
            service_principal = "ldap/ldapauth"
        _LOGGER.debug("# service principal: %s", service_principal)
        servk = gssapi.Name(
            service_principal, name_type=gssapi.NameType.kerberos_principal
        )
        self.target_name = servk
        self.ctx = gssapi.SecurityContext(
            name=servk, creds=cred, flags=sum(flags_l), usage="initiate"
        )

        try:
            initial_client_token = self.ctx.step()
        except gssapi.raw.misc.GSSError as err:
            raise errors.InterfaceError(f"Unable to initiate security context: {err}")

        _LOGGER.debug("# initial client token: %s", initial_client_token)
        return initial_client_token

    def auth_continue_krb(self, tgt_auth_challenge):
        """Continue with the Kerberos TGT service request.

        With the TGT authentication service given response generate a TGT
        service request. This method must be invoked sequentially (in a loop)
        until the security context is completed and an empty response needs to
        be send to acknowledge the server.

        Args:
            tgt_auth_challenge the challenge for the negotiation.

        Returns: tuple (bytearray TGS service request,
                        bool True if context is completed otherwise False).
        """
        _LOGGER.debug("tgt_auth challenge: %s", tgt_auth_challenge)

        resp = self.ctx.step(tgt_auth_challenge)
        _LOGGER.debug("# context step response: %s", resp)
        _LOGGER.debug("# context completed?: %s", self.ctx.complete)

        return resp, self.ctx.complete

    def auth_accept_close_handshake(self, message):
        """Accept handshake and generate closing handshake message for server.

        This method verifies the server authenticity from the given message
        and included signature and generates the closing handshake for the
        server.

        When this method is invoked the security context is already established
        and the client and server can send GSSAPI formated secure messages.

        To finish the authentication handshake the server sends a message
        with the security layer availability and the maximum buffer size.

        Since the connector only uses the GSSAPI authentication mechanism to
        authenticate the user with the server, the server will verify clients
        message signature and terminate the GSSAPI authentication and send two
        messages; an authentication acceptance b'\x01\x00\x00\x08\x01' and a
        OK packet (that must be received after sent the returned message from
        this method).

        Args:
            message a wrapped hssapi message from the server.

        Returns: bytearray closing handshake message to be send to the server.
        """
        if not self.ctx.complete:
            raise errors.ProgrammingError("Security context is not completed.")
        _LOGGER.debug("# servers message: %s", message)
        _LOGGER.debug("# GSSAPI flags in use: %s", self.ctx.actual_flags)
        try:
            unwraped = self.ctx.unwrap(message)
            _LOGGER.debug("# unwraped: %s", unwraped)
        except gssapi.raw.exceptions.BadMICError as err:
            raise errors.InterfaceError(f"Unable to unwrap server message: {err}")

        _LOGGER.debug("# unwrapped server message: %s", unwraped)
        # The message contents for the clients closing message:
        #   - security level 1 byte, must be always 1.
        #   - conciliated buffer size 3 bytes, without importance as no
        #     further GSSAPI messages will be sends.
        response = bytearray(b"\x01\x00\x00\00")
        # Closing handshake must not be encrypted.
        _LOGGER.debug("# message response: %s", response)
        wraped = self.ctx.wrap(response, encrypt=False)
        _LOGGER.debug(
            "# wrapped message response: %s, length: %d",
            wraped[0],
            len(wraped[0]),
        )

        return wraped.message

    def auth_response(self, auth_data=None):
        """This method will prepare the fist message to the server.

        Returns bytes to send to the server as the first message.
        """
        krb_service_principal = auth_data
        auth_mechanism = self._auth_data.decode()
        self.krb_service_principal = krb_service_principal
        _LOGGER.debug("read_method_name_from_server: %s", auth_mechanism)
        if auth_mechanism not in self.sasl_mechanisms:
            auth_mechanisms = '", "'.join(self.sasl_mechanisms[:-1])
            raise errors.InterfaceError(
                f'The sasl authentication method "{auth_mechanism}" requested '
                f'from the server is not supported. Only "{auth_mechanisms}" '
                f'and "{self.sasl_mechanisms[-1]}" are supported'
            )

        if b"GSSAPI" in self._auth_data:
            return self._first_message_krb()

        if self._auth_data == b"SCRAM-SHA-256":
            self.def_digest_mode = sha256

        return self._first_message()

    def _second_message(self):
        """This method generates the second message to the server

        Second message consist on the concatenation of the client and the
        server nonce, and cproof.

        c=<n,a=<user_name>>,r=<server_nonce>,p=<client_proof>
        where:
            <client_proof>: xor(<client_key>, <client_signature>)

            <client_key>: hmac(salted_password, b"Client Key")
            <client_signature>: hmac(<stored_key>, <auth_msg>)
            <stored_key>: h(<client_key>)
            <auth_msg>: <client_first_no_header>,<servers_first>,
                        c=<client_header>,r=<server_nonce>
            <client_first_no_header>: n=<username>r=<client_nonce>
        """
        if not self._auth_data:
            raise errors.InterfaceError("Missing authentication data (seed)")

        passw = self._normalize(self._password)
        salted_password = self._hi(passw, b64decode(self.server_salt), self.iterations)
        _LOGGER.debug("salted_password: %s", b64encode(salted_password).decode())

        client_key = self._hmac(salted_password, b"Client Key")
        _LOGGER.debug("client_key: %s", b64encode(client_key).decode())

        stored_key = self.def_digest_mode(client_key).digest()
        _LOGGER.debug("stored_key: %s", b64encode(stored_key).decode())

        server_key = self._hmac(salted_password, b"Server Key")
        _LOGGER.debug("server_key: %s", b64encode(server_key).decode())

        client_first_no_header = ",".join(
            [
                f"n={self._normalize(self._username)}",
                f"r={self.client_nonce}",
            ]
        )
        _LOGGER.debug("client_first_no_header: %s", client_first_no_header)

        client_header = b64encode(
            f"n,a={self._normalize(self._username)},".encode()
        ).decode()

        auth_msg = ",".join(
            [
                client_first_no_header,
                self.servers_first,
                f"c={client_header}",
                f"r={self.server_nonce}",
            ]
        )
        _LOGGER.debug("auth_msg: %s", auth_msg)

        client_signature = self._hmac(stored_key, auth_msg.encode())
        _LOGGER.debug("client_signature: %s", b64encode(client_signature).decode())

        client_proof = self._xor(client_key, client_signature)
        _LOGGER.debug("client_proof: %s", b64encode(client_proof).decode())

        self.server_auth_var = b64encode(
            self._hmac(server_key, auth_msg.encode())
        ).decode()
        _LOGGER.debug("server_auth_var: %s", self.server_auth_var)

        msg = ",".join(
            [
                f"c={client_header}",
                f"r={self.server_nonce}",
                f"p={b64encode(client_proof).decode()}",
            ]
        )
        _LOGGER.debug("second_message: %s", msg)
        return msg.encode()

    def _validate_first_reponse(self, servers_first):
        """Validates first message from the server.

        Extracts the server's salt and iterations from the servers 1st response.
        First message from the server is in the form:
            <server_salt>,i=<iterations>
        """
        if not servers_first or not isinstance(servers_first, (bytearray, bytes)):
            raise errors.InterfaceError(f"Unexpected server message: {servers_first}")
        try:
            servers_first = servers_first.decode()
            self.servers_first = servers_first
            r_server_nonce, s_salt, i_counter = servers_first.split(",")
        except ValueError:
            raise errors.InterfaceError(
                f"Unexpected server message: {servers_first}"
            ) from None
        if (
            not r_server_nonce.startswith("r=")
            or not s_salt.startswith("s=")
            or not i_counter.startswith("i=")
        ):
            raise errors.InterfaceError(
                f"Incomplete reponse from the server: {servers_first}"
            )
        if self.client_nonce in r_server_nonce:
            self.server_nonce = r_server_nonce[2:]
            _LOGGER.debug("server_nonce: %s", self.server_nonce)
        else:
            raise errors.InterfaceError(
                "Unable to authenticate response: response not well formed "
                f"{servers_first}"
            )
        self.server_salt = s_salt[2:]
        _LOGGER.debug(
            "server_salt: %s length: %s",
            self.server_salt,
            len(self.server_salt),
        )
        try:
            i_counter = i_counter[2:]
            _LOGGER.debug("iterations: %s", i_counter)
            self.iterations = int(i_counter)
        except Exception as err:
            raise errors.InterfaceError(
                f"Unable to authenticate: iterations not found {servers_first}"
            ) from err

    def auth_continue(self, servers_first_response):
        """return the second message from the client.

        Returns bytes to send to the server as the second message.
        """
        self._validate_first_reponse(servers_first_response)
        return self._second_message()

    def _validate_second_reponse(self, servers_second):
        """Validates second message from the server.

        The client and the server prove to each other they have the same Auth
        variable.

        The second message from the server consist of the server's proof:
            server_proof = HMAC(<server_key>, <auth_msg>)
            where:
                <server_key>: hmac(<salted_password>, b"Server Key")
                <auth_msg>: <client_first_no_header>,<servers_first>,
                            c=<client_header>,r=<server_nonce>

        Our server_proof must be equal to the Auth variable send on this second
        response.
        """
        if (
            not servers_second
            or not isinstance(servers_second, bytearray)
            or len(servers_second) <= 2
            or not servers_second.startswith(b"v=")
        ):
            raise errors.InterfaceError("The server's proof is not well formated")
        server_var = servers_second[2:].decode()
        _LOGGER.debug("server auth variable: %s", server_var)
        return self.server_auth_var == server_var

    def auth_finalize(self, servers_second_response):
        """finalize the authentication process.

        Raises errors.InterfaceError if the ervers_second_response is invalid.

        Returns True in successful authentication False otherwise.
        """
        if not self._validate_second_reponse(servers_second_response):
            raise errors.InterfaceError(
                "Authentication failed: Unable to proof server identity"
            )
        return True


# pylint: enable=c-extension-no-member,no-member
