authentik/passbook/providers/saml/processors/request_parser.py

"""SAML AuthNRequest Parser and dataclass"""
from base64 import b64decode
from dataclasses import dataclass
from typing import Optional
from urllib.parse import quote_plus

import xmlsec
from defusedxml import ElementTree
from lxml import etree  # nosec
from structlog import get_logger

from passbook.providers.saml.exceptions import CannotHandleAssertion
from passbook.providers.saml.models import SAMLProvider
from passbook.providers.saml.utils.encoding import decode_base64_and_inflate
from passbook.sources.saml.processors.constants import (
    DSA_SHA1,
    NS_MAP,
    NS_SAML_PROTOCOL,
    RSA_SHA1,
    RSA_SHA256,
    RSA_SHA384,
    RSA_SHA512,
    SAML_NAME_ID_FORMAT_EMAIL,
)

LOGGER = get_logger()
ERROR_SIGNATURE_REQUIRED_BUT_ABSENT = (
    "Verification Certificate configured, but request is not signed."
)
ERROR_SIGNATURE_EXISTS_BUT_NO_VERIFIER = (
    "Provider does not have a Validation Certificate configured."
)
ERROR_FAILED_TO_VERIFY = "Failed to verify signature"


@dataclass
class AuthNRequest:
    """AuthNRequest Dataclass"""

    # pylint: disable=invalid-name
    id: Optional[str] = None

    relay_state: Optional[str] = None

    name_id_policy: str = SAML_NAME_ID_FORMAT_EMAIL


class AuthNRequestParser:
    """AuthNRequest Parser"""

    provider: SAMLProvider

    def __init__(self, provider: SAMLProvider):
        self.provider = provider

    def _parse_xml(self, decoded_xml: str, relay_state: Optional[str]) -> AuthNRequest:
        root = ElementTree.fromstring(decoded_xml)

        request_acs_url = root.attrib["AssertionConsumerServiceURL"]

        if self.provider.acs_url.lower() != request_acs_url.lower():
            msg = (
                f"ACS URL of {request_acs_url} doesn't match Provider "
                f"ACS URL of {self.provider.acs_url}."
            )
            LOGGER.info(msg)
            raise CannotHandleAssertion(msg)

        auth_n_request = AuthNRequest(id=root.attrib["ID"], relay_state=relay_state)

        # Check if AuthnRequest has a NameID Policy object
        name_id_policies = root.findall(f"{{{NS_SAML_PROTOCOL}}}:NameIDPolicy")
        if len(name_id_policies) > 0:
            name_id_policy = name_id_policies[0]
            auth_n_request.name_id_policy = name_id_policy.attrib["Format"]

        return auth_n_request

    def parse(self, saml_request: str, relay_state: Optional[str]) -> AuthNRequest:
        """Validate and parse raw request with enveloped signautre."""
        decoded_xml = b64decode(saml_request.encode()).decode()

        verifier = self.provider.verification_kp

        root = etree.fromstring(decoded_xml)  # nosec
        xmlsec.tree.add_ids(root, ["ID"])
        signature_nodes = root.xpath(
            "/samlp:AuthnRequest/ds:Signature", namespaces=NS_MAP
        )
        if len(signature_nodes) != 1:
            raise CannotHandleAssertion(ERROR_SIGNATURE_REQUIRED_BUT_ABSENT)

        signature_node = signature_nodes[0]

        if verifier and signature_node is None:
            raise CannotHandleAssertion(ERROR_SIGNATURE_REQUIRED_BUT_ABSENT)

        if signature_node is not None:
            if not verifier:
                raise CannotHandleAssertion(ERROR_SIGNATURE_EXISTS_BUT_NO_VERIFIER)

            try:
                ctx = xmlsec.SignatureContext()
                key = xmlsec.Key.from_memory(
                    verifier.certificate_data,
                    xmlsec.constants.KeyDataFormatCertPem,
                    None,
                )
                ctx.key = key
                ctx.verify(signature_node)
            except xmlsec.VerificationError as exc:
                raise CannotHandleAssertion(ERROR_FAILED_TO_VERIFY) from exc

        return self._parse_xml(decoded_xml, relay_state)

    def parse_detached(
        self,
        saml_request: str,
        relay_state: Optional[str],
        signature: Optional[str] = None,
        sig_alg: Optional[str] = None,
    ) -> AuthNRequest:
        """Validate and parse raw request with detached signature"""
        decoded_xml = decode_base64_and_inflate(saml_request)

        verifier = self.provider.verification_kp

        if verifier and not (signature and sig_alg):
            raise CannotHandleAssertion(ERROR_SIGNATURE_REQUIRED_BUT_ABSENT)

        if signature and sig_alg:
            if not verifier:
                raise CannotHandleAssertion(ERROR_SIGNATURE_EXISTS_BUT_NO_VERIFIER)

            querystring = f"SAMLRequest={quote_plus(saml_request)}&"
            if relay_state is not None:
                querystring += f"RelayState={quote_plus(relay_state)}&"
            querystring += f"SigAlg={quote_plus(sig_alg)}"

            dsig_ctx = xmlsec.SignatureContext()
            key = xmlsec.Key.from_memory(
                verifier.certificate_data, xmlsec.constants.KeyDataFormatCertPem, None
            )
            dsig_ctx.key = key

            sign_algorithm_transform_map = {
                DSA_SHA1: xmlsec.constants.TransformDsaSha1,
                RSA_SHA1: xmlsec.constants.TransformRsaSha1,
                RSA_SHA256: xmlsec.constants.TransformRsaSha256,
                RSA_SHA384: xmlsec.constants.TransformRsaSha384,
                RSA_SHA512: xmlsec.constants.TransformRsaSha512,
            }
            sign_algorithm_transform = sign_algorithm_transform_map.get(
                sig_alg, xmlsec.constants.TransformRsaSha1
            )

            try:
                dsig_ctx.verify_binary(
                    querystring.encode("utf-8"),
                    sign_algorithm_transform,
                    b64decode(signature),
                )
            except xmlsec.VerificationError as exc:
                raise CannotHandleAssertion(ERROR_FAILED_TO_VERIFY) from exc
        return self._parse_xml(decoded_xml, relay_state)

    def idp_initiated(self) -> AuthNRequest:
        """Create IdP Initiated AuthNRequest"""
        return AuthNRequest()