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✏️ Editing: client_middleware_digest_auth.py

"""
Digest authentication middleware for aiohttp client.

This middleware implements HTTP Digest Authentication according to RFC 7616,
providing a more secure alternative to Basic Authentication. It supports all
standard hash algorithms including MD5, SHA, SHA-256, SHA-512 and their session
variants, as well as both 'auth' and 'auth-int' quality of protection (qop) options.
"""

import hashlib
import os
import re
import sys
import time
from collections.abc import Callable
from typing import Final, Literal, TypedDict

from yarl import URL

from . import hdrs
from .client_exceptions import ClientError
from .client_middlewares import ClientHandlerType
from .client_reqrep import ClientRequest, ClientResponse
from .payload import Payload

class DigestAuthChallenge(TypedDict, total=False):
    realm: str
    nonce: str
    qop: str
    algorithm: str
    opaque: str
    domain: str
    stale: str

DigestFunctions: dict[str, Callable[[bytes], "hashlib._Hash"]] = {
    "MD5": hashlib.md5,
    "MD5-SESS": hashlib.md5,
    "SHA": hashlib.sha1,
    "SHA-SESS": hashlib.sha1,
    "SHA256": hashlib.sha256,
    "SHA256-SESS": hashlib.sha256,
    "SHA-256": hashlib.sha256,
    "SHA-256-SESS": hashlib.sha256,
    "SHA512": hashlib.sha512,
    "SHA512-SESS": hashlib.sha512,
    "SHA-512": hashlib.sha512,
    "SHA-512-SESS": hashlib.sha512,
}

# Compile the regex pattern once at module level for performance
_HEADER_PAIRS_PATTERN = re.compile(
    r'(?:^|\s|,\s*)(\w+)\s*=\s*(?:"((?:[^"\\]|\\.)*)"|([^\s,]+))'
    if sys.version_info < (3, 11)
    else r'(?:^|\s|,\s*)((?>\w+))\s*=\s*(?:"((?:[^"\\]|\\.)*)"|([^\s,]+))'
    # +------------|--------|--|-|-|--|----|------|----|--||-----|-> Match valid start/sep
    #              +--------|--|-|-|--|----|------|----|--||-----|-> alphanumeric key (atomic
    #                       |  | | |  |    |      |    |  ||     |   group reduces backtracking)
    #                       +--|-|-|--|----|------|----|--||-----|-> maybe whitespace
    #                          | | |  |    |      |    |  ||     |
    #                          +-|-|--|----|------|----|--||-----|-> = (delimiter)
    #                            +-|--|----|------|----|--||-----|-> maybe whitespace
    #                              |  |    |      |    |  ||     |
    #                              +--|----|------|----|--||-----|-> group quoted or unquoted
    #                                 |    |      |    |  ||     |
    #                                 +----|------|----|--||-----|-> if quoted...
    #                                      +------|----|--||-----|-> anything but " or \
    #                                             +----|--||-----|-> escaped characters allowed
    #                                                  +--||-----|-> or can be empty string
    #                                                     ||     |
    #                                                     +|-----|-> if unquoted...
    #                                                      +-----|-> anything but , or <space>
    #                                                            +-> at least one char req'd
)

# RFC 7616: Challenge parameters to extract
CHALLENGE_FIELDS: Final[
    tuple[
        Literal["realm", "nonce", "qop", "algorithm", "opaque", "domain", "stale"], ...
    ]
] = (
    "realm",
    "nonce",
    "qop",
    "algorithm",
    "opaque",
    "domain",
    "stale",
)

# Supported digest authentication algorithms
# Use a tuple of sorted keys for predictable documentation and error messages
SUPPORTED_ALGORITHMS: Final[tuple[str, ...]] = tuple(sorted(DigestFunctions.keys()))

# RFC 7616: Fields that require quoting in the Digest auth header
# These fields must be enclosed in double quotes in the Authorization header.
# Algorithm, qop, and nc are never quoted per RFC specifications.
# This frozen set is used by the template-based header construction to
# automatically determine which fields need quotes.
QUOTED_AUTH_FIELDS: Final[frozenset[str]] = frozenset(
    {"username", "realm", "nonce", "uri", "response", "opaque", "cnonce"}
)

def escape_quotes(value: str) -> str:
    """Escape double quotes for HTTP header values."""
    return value.replace('"', '\\"')

def unescape_quotes(value: str) -> str:
    """Unescape double quotes in HTTP header values."""
    return value.replace('\\"', '"')

def parse_header_pairs(header: str) -> dict[str, str]:
    """
    Parse key-value pairs from WWW-Authenticate or similar HTTP headers.

This function handles the complex format of WWW-Authenticate header values,
    supporting both quoted and unquoted values, proper handling of commas in
    quoted values, and whitespace variations per RFC 7616.

Examples of supported formats:
      - key1="value1", key2=value2
      - key1 = "value1" , key2="value, with, commas"
      - key1=value1,key2="value2"
      - realm="example.com", nonce="12345", qop="auth"

Args:
        header: The header value string to parse

Returns:
        Dictionary mapping parameter names to their values
    """
    return {
        stripped_key: unescape_quotes(quoted_val) if quoted_val else unquoted_val
        for key, quoted_val, unquoted_val in _HEADER_PAIRS_PATTERN.findall(header)
        if (stripped_key := key.strip())
    }

class DigestAuthMiddleware:
    """
    HTTP digest authentication middleware for aiohttp client.

This middleware intercepts 401 Unauthorized responses containing a Digest
    authentication challenge, calculates the appropriate digest credentials,
    and automatically retries the request with the proper Authorization header.

Features:
    - Handles all aspects of Digest authentication handshake automatically
    - Supports all standard hash algorithms:
      - MD5, MD5-SESS
      - SHA, SHA-SESS
      - SHA256, SHA256-SESS, SHA-256, SHA-256-SESS
      - SHA512, SHA512-SESS, SHA-512, SHA-512-SESS
    - Supports 'auth' and 'auth-int' quality of protection modes
    - Properly handles quoted strings and parameter parsing
    - Includes replay attack protection with client nonce count tracking
    - Supports preemptive authentication per RFC 7616 Section 3.6

Origin scoping:
    The credentials are scoped to the origin of the first request the
    middleware handles. A request to a different origin is passed through
    untouched, so it never receives a digest response computed from those
    credentials, unless that origin falls within a protection space the
    anchor origin advertised through the RFC 7616 ``domain`` directive. Make
    the first request through the middleware against the intended origin, as
    the anchor is pinned to it and not reset for the life of the instance.

Standards compliance:
    - RFC 7616: HTTP Digest Access Authentication (primary reference)
    - RFC 2617: HTTP Authentication (deprecated by RFC 7616)
    - RFC 1945: Section 11.1 (username restrictions)

Implementation notes:
    The core digest calculation is inspired by the implementation in
    https://github.com/requests/requests/blob/v2.18.4/requests/auth.py
    with added support for modern digest auth features and error handling.
    """

def __init__(
        self,
        login: str,
        password: str,
        preemptive: bool = True,
    ) -> None:
        if login is None:
            raise ValueError("None is not allowed as login value")

if password is None:
            raise ValueError("None is not allowed as password value")

if ":" in login:
            raise ValueError('A ":" is not allowed in username (RFC 1945#section-11.1)')

self._login_str: Final[str] = login
        self._login_bytes: Final[bytes] = login.encode("utf-8")
        self._password_bytes: Final[bytes] = password.encode("utf-8")

self._last_nonce_bytes = b""
        self._nonce_count = 0
        self._challenge: DigestAuthChallenge = {}
        self._preemptive: bool = preemptive
        # Set of URLs defining the protection space
        self._protection_space: list[str] = []
        # Origin the credentials are scoped to; set on the first request.
        self._origin: URL | None = None

async def _encode(self, method: str, url: URL, body: Payload | Literal[b""]) -> str:
        """
        Build digest authorization header for the current challenge.

Args:
            method: The HTTP method (GET, POST, etc.)
            url: The request URL
            body: The request body (used for qop=auth-int)

Returns:
            A fully formatted Digest authorization header string

Raises:
            ClientError: If the challenge is missing required parameters or
                         contains unsupported values

"""
        challenge = self._challenge
        if "realm" not in challenge:
            raise ClientError(
                "Malformed Digest auth challenge: Missing 'realm' parameter"
            )

if "nonce" not in challenge:
            raise ClientError(
                "Malformed Digest auth challenge: Missing 'nonce' parameter"
            )

# Empty realm values are allowed per RFC 7616 (SHOULD, not MUST, contain host name)
        realm = challenge["realm"]
        nonce = challenge["nonce"]

# Empty nonce values are not allowed as they are security-critical for replay protection
        if not nonce:
            raise ClientError(
                "Security issue: Digest auth challenge contains empty 'nonce' value"
            )

qop_raw = challenge.get("qop", "")
        # Preserve original algorithm case for response while using uppercase for processing
        algorithm_original = challenge.get("algorithm", "MD5")
        algorithm = algorithm_original.upper()
        opaque = challenge.get("opaque", "")

# Convert string values to bytes once
        nonce_bytes = nonce.encode("utf-8")
        realm_bytes = realm.encode("utf-8")
        # Use the encoded request-target (raw_path_qs) since that is what is
        # transmitted on the wire and what the server signs against. Using the
        # decoded form would cause digest verification to fail when the path
        # or query string contains percent-encoded reserved characters.
        path = URL(url).raw_path_qs

# Process QoP
        qop = ""
        qop_bytes = b""
        if qop_raw:
            valid_qops = {"auth", "auth-int"}.intersection(
                {q.strip() for q in qop_raw.split(",") if q.strip()}
            )
            if not valid_qops:
                raise ClientError(
                    f"Digest auth error: Unsupported Quality of Protection (qop) value(s): {qop_raw}"
                )

qop = "auth-int" if "auth-int" in valid_qops else "auth"
            qop_bytes = qop.encode("utf-8")

if algorithm not in DigestFunctions:
            raise ClientError(
                f"Digest auth error: Unsupported hash algorithm: {algorithm}. "
                f"Supported algorithms: {', '.join(SUPPORTED_ALGORITHMS)}"
            )
        hash_fn: Final = DigestFunctions[algorithm]

def H(x: bytes) -> bytes:
            """RFC 7616 Section 3: Hash function H(data) = hex(hash(data))."""
            return hash_fn(x).hexdigest().encode()

def KD(s: bytes, d: bytes) -> bytes:
            """RFC 7616 Section 3: KD(secret, data) = H(concat(secret, ":", data))."""
            return H(b":".join((s, d)))

# Calculate A1 and A2
        A1 = b":".join((self._login_bytes, realm_bytes, self._password_bytes))
        A2 = f"{method.upper()}:{path}".encode()
        if qop == "auth-int":
            if isinstance(body, Payload):  # will always be empty bytes unless Payload
                entity_bytes = await body.as_bytes()  # Get bytes from Payload
            else:
                entity_bytes = body
            entity_hash = H(entity_bytes)
            A2 = b":".join((A2, entity_hash))

HA1 = H(A1)
        HA2 = H(A2)

# Nonce count handling
        if nonce_bytes == self._last_nonce_bytes:
            self._nonce_count += 1
        else:
            self._nonce_count = 1

self._last_nonce_bytes = nonce_bytes
        ncvalue = f"{self._nonce_count:08x}"
        ncvalue_bytes = ncvalue.encode("utf-8")

# Generate client nonce
        cnonce = hashlib.sha1(
            b"".join(
                [
                    str(self._nonce_count).encode("utf-8"),
                    nonce_bytes,
                    time.ctime().encode("utf-8"),
                    os.urandom(8),
                ]
            )
        ).hexdigest()[:16]
        cnonce_bytes = cnonce.encode("utf-8")

# Special handling for session-based algorithms
        if algorithm.upper().endswith("-SESS"):
            HA1 = H(b":".join((HA1, nonce_bytes, cnonce_bytes)))

# Calculate the response digest
        if qop:
            noncebit = b":".join(
                (nonce_bytes, ncvalue_bytes, cnonce_bytes, qop_bytes, HA2)
            )
            response_digest = KD(HA1, noncebit)
        else:
            response_digest = KD(HA1, b":".join((nonce_bytes, HA2)))

# Define a dict mapping of header fields to their values
        # Group fields into always-present, optional, and qop-dependent
        header_fields = {
            # Always present fields
            "username": escape_quotes(self._login_str),
            "realm": escape_quotes(realm),
            "nonce": escape_quotes(nonce),
            "uri": path,
            "response": response_digest.decode(),
            "algorithm": algorithm_original,
        }

# Optional fields
        if opaque:
            header_fields["opaque"] = escape_quotes(opaque)

# QoP-dependent fields
        if qop:
            header_fields["qop"] = qop
            header_fields["nc"] = ncvalue
            header_fields["cnonce"] = cnonce

# Build header using templates for each field type
        pairs: list[str] = []
        for field, value in header_fields.items():
            if field in QUOTED_AUTH_FIELDS:
                pairs.append(f'{field}="{value}"')
            else:
                pairs.append(f"{field}={value}")

return f"Digest {', '.join(pairs)}"

def _in_protection_space(self, url: URL) -> bool:
        """
        Check if the given URL is within the current protection space.

According to RFC 7616, a URI is in the protection space if any URI
        in the protection space is a prefix of it (after both have been made absolute).
        """
        request_str = str(url)
        for space_str in self._protection_space:
            # Check if request starts with space URL
            if not request_str.startswith(space_str):
                continue
            # Exact match or space ends with / (proper directory prefix)
            if len(request_str) == len(space_str) or space_str[-1] == "/":
                return True
            # Check next char is / to ensure proper path boundary
            if request_str[len(space_str)] == "/":
                return True
        return False

def _authenticate(self, response: ClientResponse) -> bool:
        """
        Takes the given response and tries digest-auth, if needed.

Returns true if the original request must be resent.
        """
        if response.status != 401:
            return False

auth_header = response.headers.get("www-authenticate", "")
        if not auth_header:
            return False  # No authentication header present

method, sep, headers = auth_header.partition(" ")
        if not sep:
            # No space found in www-authenticate header
            return False  # Malformed auth header, missing scheme separator

if method.lower() != "digest":
            # Not a digest auth challenge (could be Basic, Bearer, etc.)
            return False

if not headers:
            # We have a digest scheme but no parameters
            return False  # Malformed digest header, missing parameters

# We have a digest auth header with content
        if not (header_pairs := parse_header_pairs(headers)):
            # Failed to parse any key-value pairs
            return False  # Malformed digest header, no valid parameters

# Extract challenge parameters
        self._challenge = {}
        for field in CHALLENGE_FIELDS:
            if (value := header_pairs.get(field)) is not None:
                self._challenge[field] = value

# Update protection space based on domain parameter or default to origin
        origin = response.url.origin()

if domain := self._challenge.get("domain"):
            # Parse space-separated list of URIs
            self._protection_space = []
            for uri in domain.split():
                # Remove quotes if present
                uri = uri.strip('"')
                if uri.startswith("/"):
                    # Path-absolute, relative to origin
                    self._protection_space.append(str(origin.join(URL(uri))))
                else:
                    # Absolute URI
                    self._protection_space.append(str(URL(uri)))
        else:
            # No domain specified, protection space is entire origin
            self._protection_space = [str(origin)]

# Return True only if we found at least one challenge parameter
        return bool(self._challenge)

async def __call__(
        self, request: ClientRequest, handler: ClientHandlerType
    ) -> ClientResponse:
        """Run the digest auth middleware."""
        # Credentials are scoped to the first request's origin. Other origins
        # pass through untouched unless a challenge from the anchor origin
        # advertised them via RFC 7616 domain; mirrors aiohttp stripping
        # Authorization on cross-origin redirects.
        origin = request.url.origin()
        if self._origin is None:
            self._origin = origin
        elif origin != self._origin and not self._in_protection_space(request.url):
            return await handler(request)

response = None
        for retry_count in range(2):
            # Apply authorization header if:
            # 1. This is a retry after 401 (retry_count > 0), OR
            # 2. Preemptive auth is enabled AND we have a challenge AND the URL is in protection space
            if retry_count > 0 or (
                self._preemptive
                and self._challenge
                and self._in_protection_space(request.url)
            ):
                request.headers[hdrs.AUTHORIZATION] = await self._encode(
                    request.method, request.url, request.body
                )

# Send the request
            response = await handler(request)

# Check if we need to authenticate
            if not self._authenticate(response):
                break

# At this point, response is guaranteed to be defined
        assert response is not None
        return response

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