"""
Helper classes for SSPI authentication via the win32security module.

SSPI authentication involves a token-exchange "dance", the exact details
of which depends on the authentication provider used.  There are also
a number of complex flags and constants that need to be used - in most
cases, there are reasonable defaults.

These classes attempt to hide these details from you until you really need
to know.  They are not designed to handle all cases, just the common ones.
If you need finer control than offered here, just use the win32security
functions directly.
"""
# Based on Roger Upole's sspi demos.
# $Id$
import win32security, sspicon

error = win32security.error

class _BaseAuth(object):
    def __init__(self):
        self.reset()

    def reset(self):
        """Reset everything to an unauthorized state"""
        self.ctxt = None
        self.authenticated = False
        self.initiator_name = None
        self.service_name = None

        # The next seq_num for an encrypt/sign operation
        self.next_seq_num = 0

    def _get_next_seq_num(self):
        """Get the next sequence number for a transmission.  Default
        implementation is to increment a counter
        """
        ret = self.next_seq_num
        self.next_seq_num = self.next_seq_num + 1
        return ret

    def encrypt(self, data):
        """Encrypt a string, returning a tuple of (encrypted_data, trailer).
        These can be passed to decrypt to get back the original string.
        """
        pkg_size_info=self.ctxt.QueryContextAttributes(sspicon.SECPKG_ATTR_SIZES)
        trailersize=pkg_size_info['SecurityTrailer']

        encbuf=win32security.PySecBufferDescType()
        encbuf.append(win32security.PySecBufferType(len(data), sspicon.SECBUFFER_DATA))
        encbuf.append(win32security.PySecBufferType(trailersize, sspicon.SECBUFFER_TOKEN))
        encbuf[0].Buffer=data
        self.ctxt.EncryptMessage(0,encbuf,self._get_next_seq_num())
        return encbuf[0].Buffer, encbuf[1].Buffer

    def decrypt(self, data, trailer):
        """Decrypt a previously encrypted string, returning the orignal data"""
        encbuf=win32security.PySecBufferDescType()
        encbuf.append(win32security.PySecBufferType(len(data), sspicon.SECBUFFER_DATA))
        encbuf.append(win32security.PySecBufferType(len(trailer), sspicon.SECBUFFER_TOKEN))
        encbuf[0].Buffer=data
        encbuf[1].Buffer=trailer
        self.ctxt.DecryptMessage(encbuf,self._get_next_seq_num())
        return encbuf[0].Buffer

    def sign(self, data):
        """sign a string suitable for transmission, returning the signature.
        Passing the data and signature to verify will determine if the data
        is unchanged.
        """
        pkg_size_info=self.ctxt.QueryContextAttributes(sspicon.SECPKG_ATTR_SIZES)
        sigsize=pkg_size_info['MaxSignature']
        sigbuf=win32security.PySecBufferDescType()
        sigbuf.append(win32security.PySecBufferType(len(data), sspicon.SECBUFFER_DATA))
        sigbuf.append(win32security.PySecBufferType(sigsize, sspicon.SECBUFFER_TOKEN))
        sigbuf[0].Buffer=data

        self.ctxt.MakeSignature(0,sigbuf,self._get_next_seq_num())
        return sigbuf[1].Buffer

    def verify(self, data, sig):
        """Verifies data and its signature.  If verification fails, an sspi.error
        will be raised.
        """
        sigbuf=win32security.PySecBufferDescType()
        sigbuf.append(win32security.PySecBufferType(len(data), sspicon.SECBUFFER_DATA))
        sigbuf.append(win32security.PySecBufferType(len(sig), sspicon.SECBUFFER_TOKEN))

        sigbuf[0].Buffer=data
        sigbuf[1].Buffer=sig
        self.ctxt.VerifySignature(sigbuf,self._get_next_seq_num())

    def unwrap(self, token):
        """
            GSSAPI's unwrap with SSPI.
            https://docs.microsoft.com/en-us/windows/win32/secauthn/sspi-kerberos-interoperability-with-gssapi

            Usable mainly with Kerberos SSPI package, but this is not enforced.

            Return the clear text, and a boolean that is True if the token was encrypted.
        """
        buffer = win32security.PySecBufferDescType()
        # This buffer will contain a "stream", which is the token coming from the other side
        buffer.append(win32security.PySecBufferType(len(token), sspicon.SECBUFFER_STREAM))
        buffer[0].Buffer = token

        # This buffer will receive the clear, or just unwrapped text if no encryption was used.
        # Will be resized by the lib.
        buffer.append(win32security.PySecBufferType(0, sspicon.SECBUFFER_DATA))

        pfQOP = self.ctxt.DecryptMessage(buffer, self._get_next_seq_num())

        r = buffer[1].Buffer
        return r, not (pfQOP == sspicon.SECQOP_WRAP_NO_ENCRYPT)

    def wrap(self, msg, encrypt=False):
        """
            GSSAPI's wrap with SSPI.
            https://docs.microsoft.com/en-us/windows/win32/secauthn/sspi-kerberos-interoperability-with-gssapi

            Usable mainly with Kerberos SSPI package, but this is not enforced.

            Wrap a message to be sent to the other side. Encrypted if encrypt is True.
        """

        size_info = self.ctxt.QueryContextAttributes(sspicon.SECPKG_ATTR_SIZES)
        trailer_size = size_info['SecurityTrailer']
        block_size = size_info['BlockSize']

        buffer = win32security.PySecBufferDescType()

        # This buffer will contain unencrypted data to wrap, and maybe encrypt.
        buffer.append(win32security.PySecBufferType(len(msg), sspicon.SECBUFFER_DATA))
        buffer[0].Buffer = msg

        # Will receive the token that forms the beginning of the msg
        buffer.append(win32security.PySecBufferType(trailer_size, sspicon.SECBUFFER_TOKEN))

        # The trailer is needed in case of block encryption
        buffer.append(win32security.PySecBufferType(block_size, sspicon.SECBUFFER_PADDING))

        fQOP = 0 if encrypt else sspicon.SECQOP_WRAP_NO_ENCRYPT
        self.ctxt.EncryptMessage(fQOP, buffer, self._get_next_seq_num())

        # Sec token, then data, then padding
        r = buffer[1].Buffer + buffer[0].Buffer + buffer[2].Buffer
        return r

    def _amend_ctx_name(self):
        """Adds initiator and service names in the security context for ease of use"""
        if not self.authenticated:
            raise ValueError("Sec context is not completely authenticated")

        try:
            names = self.ctxt.QueryContextAttributes(sspicon.SECPKG_ATTR_NATIVE_NAMES)
        except error:
            # The SSP doesn't provide these attributes.
            pass
        else:
            self.initiator_name, self.service_name = names


class ClientAuth(_BaseAuth):
    """Manages the client side of an SSPI authentication handshake
    """
    def __init__(self,
                 pkg_name, # Name of the package to used.
                 client_name = None, # User for whom credentials are used.
                 auth_info = None, # or a tuple of (username, domain, password)
                 targetspn = None, # Target security context provider name.
                 scflags=None, # security context flags
                 datarep=sspicon.SECURITY_NETWORK_DREP):
        if scflags is None:
            scflags = sspicon.ISC_REQ_INTEGRITY|sspicon.ISC_REQ_SEQUENCE_DETECT|\
                      sspicon.ISC_REQ_REPLAY_DETECT|sspicon.ISC_REQ_CONFIDENTIALITY
        self.scflags=scflags
        self.datarep=datarep
        self.targetspn=targetspn
        self.pkg_info=win32security.QuerySecurityPackageInfo(pkg_name)
        self.credentials, \
        self.credentials_expiry=win32security.AcquireCredentialsHandle(
                client_name, self.pkg_info['Name'],
                sspicon.SECPKG_CRED_OUTBOUND,
                None, auth_info)
        _BaseAuth.__init__(self)


    def authorize(self, sec_buffer_in):
        """Perform *one* step of the client authentication process. Pass None for the first round"""
        if sec_buffer_in is not None and type(sec_buffer_in) != win32security.PySecBufferDescType:
            # User passed us the raw data - wrap it into a SecBufferDesc
            sec_buffer_new=win32security.PySecBufferDescType()
            tokenbuf=win32security.PySecBufferType(self.pkg_info['MaxToken'],
                                                   sspicon.SECBUFFER_TOKEN)
            tokenbuf.Buffer=sec_buffer_in
            sec_buffer_new.append(tokenbuf)
            sec_buffer_in = sec_buffer_new
        sec_buffer_out=win32security.PySecBufferDescType()
        tokenbuf=win32security.PySecBufferType(self.pkg_info['MaxToken'], sspicon.SECBUFFER_TOKEN)
        sec_buffer_out.append(tokenbuf)
        ## input context handle should be NULL on first call
        ctxtin=self.ctxt
        if self.ctxt is None:
            self.ctxt=win32security.PyCtxtHandleType()
        err, attr, exp=win32security.InitializeSecurityContext(
            self.credentials,
            ctxtin,
            self.targetspn,
            self.scflags,
            self.datarep,
            sec_buffer_in,
            self.ctxt,
            sec_buffer_out)
        # Stash these away incase someone needs to know the state from the
        # final call.
        self.ctxt_attr = attr
        self.ctxt_expiry = exp
        
        if err in (sspicon.SEC_I_COMPLETE_NEEDED,sspicon.SEC_I_COMPLETE_AND_CONTINUE):
            self.ctxt.CompleteAuthToken(sec_buffer_out)

        self.authenticated = err == 0
        if self.authenticated:
            self._amend_ctx_name()

        return err, sec_buffer_out

class ServerAuth(_BaseAuth):
    """Manages the server side of an SSPI authentication handshake
    """
    def __init__(self,
                 pkg_name,
                 spn = None,
                 scflags=None,
                 datarep=sspicon.SECURITY_NETWORK_DREP):
        self.spn=spn
        self.datarep=datarep
        
        if scflags is None:
            scflags = sspicon.ASC_REQ_INTEGRITY|sspicon.ASC_REQ_SEQUENCE_DETECT|\
                      sspicon.ASC_REQ_REPLAY_DETECT|sspicon.ASC_REQ_CONFIDENTIALITY
        # Should we default to sspicon.KerbAddExtraCredentialsMessage
        # if pkg_name=='Kerberos'?
        self.scflags=scflags

        self.pkg_info=win32security.QuerySecurityPackageInfo(pkg_name)

        self.credentials, \
        self.credentials_expiry=win32security.AcquireCredentialsHandle(spn,
                self.pkg_info['Name'], sspicon.SECPKG_CRED_INBOUND, None, None)
        _BaseAuth.__init__(self)

    def authorize(self, sec_buffer_in):
        """Perform *one* step of the server authentication process."""
        if sec_buffer_in is not None and type(sec_buffer_in) != win32security.PySecBufferDescType:
            # User passed us the raw data - wrap it into a SecBufferDesc
            sec_buffer_new=win32security.PySecBufferDescType()
            tokenbuf=win32security.PySecBufferType(self.pkg_info['MaxToken'],
                                                   sspicon.SECBUFFER_TOKEN)
            tokenbuf.Buffer=sec_buffer_in
            sec_buffer_new.append(tokenbuf)
            sec_buffer_in = sec_buffer_new

        sec_buffer_out=win32security.PySecBufferDescType()
        tokenbuf=win32security.PySecBufferType(self.pkg_info['MaxToken'], sspicon.SECBUFFER_TOKEN)
        sec_buffer_out.append(tokenbuf)
        ## input context handle is None initially, then handle returned from last call thereafter
        ctxtin=self.ctxt
        if self.ctxt is None:
            self.ctxt=win32security.PyCtxtHandleType()
        err, attr, exp = win32security.AcceptSecurityContext(self.credentials, ctxtin,
            sec_buffer_in, self.scflags,
            self.datarep, self.ctxt, sec_buffer_out)

        # Stash these away incase someone needs to know the state from the
        # final call.
        self.ctxt_attr = attr
        self.ctxt_expiry = exp

        if err in (sspicon.SEC_I_COMPLETE_NEEDED,sspicon.SEC_I_COMPLETE_AND_CONTINUE):
            self.ctxt.CompleteAuthToken(sec_buffer_out)

        self.authenticated = err == 0
        if self.authenticated:
            self._amend_ctx_name()

        return err, sec_buffer_out

if __name__=='__main__':
    # This is the security package (the security support provider / the security backend)
    # we want to use for this example.
    ssp = "Kerberos"  # or "NTLM" or "Negotiate" which enable negotiation between
                      # Kerberos (prefered) and NTLM (if not supported on the other side).

    flags = (
        sspicon.ISC_REQ_MUTUAL_AUTH |      # mutual authentication
        sspicon.ISC_REQ_INTEGRITY |        # check for integrity
        sspicon.ISC_REQ_SEQUENCE_DETECT |  # enable out-of-order messages
        sspicon.ISC_REQ_CONFIDENTIALITY |  # request confidentiality
        sspicon.ISC_REQ_REPLAY_DETECT      # request replay detection
    )

    # Get our identity, mandatory for the Kerberos case *for this example*
    # Kerberos cannot be used if we don't tell it the target we want
    # to authenticate to.
    cred_handle, exp = win32security.AcquireCredentialsHandle(
        None, ssp, sspicon.SECPKG_CRED_INBOUND, None, None
    )
    cred = cred_handle.QueryCredentialsAttributes(sspicon.SECPKG_CRED_ATTR_NAMES)
    print("We are:", cred)

    # Setup the 2 contexts. In real life, only one is needed: the other one is
    # created in the process we want to communicate with.
    sspiclient=ClientAuth(ssp, scflags=flags, targetspn=cred)
    sspiserver=ServerAuth(ssp, scflags=flags)

    print("SSP : %s (%s)" % (sspiclient.pkg_info["Name"], sspiclient.pkg_info["Comment"]))

    # Perform the authentication dance, each loop exchanging more information
    # on the way to completing authentication.
    sec_buffer=None
    client_step = 0
    server_step = 0
    while not(sspiclient.authenticated) or len(sec_buffer[0].Buffer):
        client_step += 1
        err, sec_buffer = sspiclient.authorize(sec_buffer)
        print("Client step %s" % client_step)
        if sspiserver.authenticated and len(sec_buffer[0].Buffer) == 0:
            break

        server_step += 1
        err, sec_buffer = sspiserver.authorize(sec_buffer)
        print("Server step %s" % server_step)

    # Authentication process is finished.
    print("Initiator name from the service side:", sspiserver.initiator_name)
    print("Service name from the client side:   ", sspiclient.service_name)

    data = "hello".encode("ascii") # py3k-friendly

    # Simple signature, not compatible with GSSAPI.
    sig = sspiclient.sign(data)
    sspiserver.verify(data, sig)

    # Encryption
    encrypted, sig = sspiclient.encrypt(data)
    decrypted = sspiserver.decrypt(encrypted, sig)
    assert decrypted == data

    # GSSAPI wrapping, no encryption (NTLM always encrypts)
    wrapped = sspiclient.wrap(data)
    unwrapped, was_encrypted = sspiserver.unwrap(wrapped)
    print("encrypted ?", was_encrypted)
    assert data == unwrapped

    # GSSAPI wrapping, with encryption
    wrapped = sspiserver.wrap(data, encrypt=True)
    unwrapped, was_encrypted = sspiclient.unwrap(wrapped)
    print("encrypted ?", was_encrypted)
    assert data == unwrapped

    print("cool!")
