microblog.pub/app/httpsig.py

354 lines
12 KiB
Python

import base64
import hashlib
import json
import typing
from dataclasses import dataclass
from datetime import datetime
from datetime import timedelta
from datetime import timezone
from typing import Any
from typing import Dict
from typing import MutableMapping
from typing import Optional
from urllib.parse import urlparse
import fastapi
import httpx
from cachetools import LFUCache
from Crypto.Hash import SHA256
from Crypto.Signature import PKCS1_v1_5
from dateutil.parser import parse
from loguru import logger
from sqlalchemy import select
from app import activitypub as ap
from app import config
from app.config import BLOCKED_SERVERS
from app.config import KEY_PATH
from app.database import AsyncSession
from app.database import get_db_session
from app.key import Key
from app.utils.datetime import now
_KEY_CACHE: MutableMapping[str, Key] = LFUCache(256)
def _build_signed_string(
signed_headers: str,
method: str,
path: str,
headers: Any,
body_digest: str | None,
sig_data: dict[str, Any],
) -> tuple[str, datetime | None]:
signature_date: datetime | None = None
out = []
for signed_header in signed_headers.split(" "):
if signed_header == "(created)":
signature_date = datetime.fromtimestamp(int(sig_data["created"])).replace(
tzinfo=timezone.utc
)
elif signed_header == "date":
signature_date = parse(headers["date"])
if signed_header == "(request-target)":
out.append("(request-target): " + method.lower() + " " + path)
elif signed_header == "digest" and body_digest:
out.append("digest: " + body_digest)
elif signed_header in ["(created)", "(expires)"]:
out.append(
signed_header
+ ": "
+ sig_data[signed_header[1 : len(signed_header) - 1]]
)
else:
out.append(signed_header + ": " + headers[signed_header])
return "\n".join(out), signature_date
def _parse_sig_header(val: Optional[str]) -> Optional[Dict[str, str]]:
if not val:
return None
out = {}
for data in val.split(","):
k, v = data.split("=", 1)
out[k] = v[1 : len(v) - 1] # noqa: black conflict
return out
def _verify_h(signed_string, signature, pubkey):
signer = PKCS1_v1_5.new(pubkey)
digest = SHA256.new()
digest.update(signed_string.encode("utf-8"))
return signer.verify(digest, signature)
def _body_digest(body: bytes) -> str:
h = hashlib.new("sha256")
h.update(body) # type: ignore
return "SHA-256=" + base64.b64encode(h.digest()).decode("utf-8")
async def _get_public_key(
db_session: AsyncSession,
key_id: str,
should_skip_cache: bool = False,
) -> Key:
if not should_skip_cache and (cached_key := _KEY_CACHE.get(key_id)):
logger.info(f"Key {key_id} found in cache")
return cached_key
# Check if the key belongs to an actor already in DB
from app import models
existing_actor = (
await db_session.scalars(
select(models.Actor).where(models.Actor.ap_id == key_id.split("#")[0])
)
).one_or_none()
if not should_skip_cache:
if existing_actor and existing_actor.public_key_id == key_id:
k = Key(existing_actor.ap_id, key_id)
k.load_pub(existing_actor.public_key_as_pem)
logger.info(f"Found {key_id} on an existing actor")
_KEY_CACHE[key_id] = k
return k
# Fetch it
from app import activitypub as ap
from app.actor import RemoteActor
from app.actor import update_actor_if_needed
# Without signing the request as if it's the first contact, the 2 servers
# might race to fetch each other key
try:
actor = await ap.fetch(key_id, disable_httpsig=True)
except ap.ObjectUnavailableError:
actor = await ap.fetch(key_id, disable_httpsig=False)
if actor["type"] == "Key":
# The Key is not embedded in the Person
k = Key(actor["owner"], actor["id"])
k.load_pub(actor["publicKeyPem"])
else:
k = Key(actor["id"], actor["publicKey"]["id"])
k.load_pub(actor["publicKey"]["publicKeyPem"])
# Ensure the right key was fetch
# TODO: some server have the key ID `http://` but fetching it return `https`
if key_id not in [k.key_id(), k.owner]:
raise ValueError(
f"failed to fetch requested key {key_id}: got {actor['publicKey']}"
)
if should_skip_cache and actor["type"] != "Key" and existing_actor:
# We had to skip the cache, which means the actor key probably changed
# and we want to update our cached version
await update_actor_if_needed(db_session, existing_actor, RemoteActor(actor))
await db_session.commit()
_KEY_CACHE[key_id] = k
return k
@dataclass(frozen=True)
class HTTPSigInfo:
has_valid_signature: bool
signed_by_ap_actor_id: str | None = None
is_ap_actor_gone: bool = False
is_unsupported_algorithm: bool = False
is_expired: bool = False
is_from_blocked_server: bool = False
server: str | None = None
async def httpsig_checker(
request: fastapi.Request,
db_session: AsyncSession = fastapi.Depends(get_db_session),
) -> HTTPSigInfo:
body = await request.body()
hsig = _parse_sig_header(request.headers.get("Signature"))
if not hsig:
logger.info("No HTTP signature found")
return HTTPSigInfo(has_valid_signature=False)
try:
key_id = hsig["keyId"]
except KeyError:
logger.info("Missing keyId")
return HTTPSigInfo(
has_valid_signature=False,
)
server = urlparse(key_id).hostname
if server in BLOCKED_SERVERS:
return HTTPSigInfo(
has_valid_signature=False,
server=server,
is_from_blocked_server=True,
)
if alg := hsig.get("algorithm") not in ["rsa-sha256", "hs2019"]:
logger.info(f"Unsupported HTTP sig algorithm: {alg}")
return HTTPSigInfo(
has_valid_signature=False,
is_unsupported_algorithm=True,
server=server,
)
# Try to drop Delete activity spams early on, this prevent making an extra
# HTTP requests trying to fetch an unavailable actor to verify the HTTP sig
try:
if request.method == "POST" and request.url.path.endswith("/inbox"):
from app import models # TODO: solve this circular import
activity = json.loads(body)
actor_id = ap.get_id(activity["actor"])
if (
ap.as_list(activity["type"])[0] == "Delete"
and actor_id == ap.get_id(activity["object"])
and not (
await db_session.scalars(
select(models.Actor).where(
models.Actor.ap_id == actor_id,
)
)
).one_or_none()
):
logger.info(f"Dropping Delete activity early for {body=}")
raise fastapi.HTTPException(status_code=202)
except fastapi.HTTPException as http_exc:
raise http_exc
except Exception:
logger.exception("Failed to check for Delete spam")
# logger.debug(f"hsig={hsig}")
signed_string, signature_date = _build_signed_string(
hsig["headers"],
request.method,
request.url.path,
request.headers,
_body_digest(body) if body else None,
hsig,
)
# Sanity checks on the signature date
if signature_date is None or now() - signature_date > timedelta(hours=12):
logger.info(f"Signature expired: {signature_date=}")
return HTTPSigInfo(
has_valid_signature=False,
is_expired=True,
server=server,
)
try:
k = await _get_public_key(db_session, hsig["keyId"])
except (ap.ObjectIsGoneError, ap.ObjectNotFoundError):
logger.info("Actor is gone or not found")
return HTTPSigInfo(has_valid_signature=False, is_ap_actor_gone=True)
except Exception:
logger.exception(f'Failed to fetch HTTP sig key {hsig["keyId"]}')
return HTTPSigInfo(has_valid_signature=False)
has_valid_signature = _verify_h(
signed_string, base64.b64decode(hsig["signature"]), k.pubkey
)
# If the signature is not valid, we may have to update the cached actor
if not has_valid_signature:
logger.info("Invalid signature, trying to refresh actor")
try:
k = await _get_public_key(db_session, hsig["keyId"], should_skip_cache=True)
has_valid_signature = _verify_h(
signed_string, base64.b64decode(hsig["signature"]), k.pubkey
)
except Exception:
logger.exception("Failed to refresh actor")
httpsig_info = HTTPSigInfo(
has_valid_signature=has_valid_signature,
signed_by_ap_actor_id=k.owner,
server=server,
)
logger.info(f"Valid HTTP signature for {httpsig_info.signed_by_ap_actor_id}")
return httpsig_info
async def enforce_httpsig(
request: fastapi.Request,
httpsig_info: HTTPSigInfo = fastapi.Depends(httpsig_checker),
) -> HTTPSigInfo:
"""FastAPI Depends"""
if httpsig_info.is_from_blocked_server:
logger.warning(f"{httpsig_info.server} is blocked")
raise fastapi.HTTPException(status_code=403, detail="Blocked")
if not httpsig_info.has_valid_signature:
logger.warning(f"Invalid HTTP sig {httpsig_info=}")
body = await request.body()
logger.info(f"{body=}")
# Special case for Mastoodon instance that keep resending Delete
# activities for actor we don't know about if we raise a 401
if httpsig_info.is_ap_actor_gone:
logger.info("Let's make Mastodon happy, returning a 202")
raise fastapi.HTTPException(status_code=202)
detail = "Invalid HTTP sig"
if httpsig_info.is_unsupported_algorithm:
detail = "Unsupported signature algorithm, must be rsa-sha256 or hs2019"
elif httpsig_info.is_expired:
detail = "Signature expired"
raise fastapi.HTTPException(status_code=401, detail=detail)
return httpsig_info
class HTTPXSigAuth(httpx.Auth):
def __init__(self, key: Key) -> None:
self.key = key
def auth_flow(
self, r: httpx.Request
) -> typing.Generator[httpx.Request, httpx.Response, None]:
logger.info(f"keyid={self.key.key_id()}")
bodydigest = None
if r.content:
bh = hashlib.new("sha256")
bh.update(r.content)
bodydigest = "SHA-256=" + base64.b64encode(bh.digest()).decode("utf-8")
date = datetime.utcnow().strftime("%a, %d %b %Y %H:%M:%S GMT")
r.headers["Date"] = date
if bodydigest:
r.headers["Digest"] = bodydigest
sigheaders = "(request-target) user-agent host date digest content-type"
else:
sigheaders = "(request-target) user-agent host date accept"
to_be_signed, _ = _build_signed_string(
sigheaders, r.method, r.url.path, r.headers, bodydigest, {}
)
if not self.key.privkey:
raise ValueError("Should never happen")
signer = PKCS1_v1_5.new(self.key.privkey)
digest = SHA256.new()
digest.update(to_be_signed.encode("utf-8"))
sig = base64.b64encode(signer.sign(digest)).decode()
key_id = self.key.key_id()
sig_value = f'keyId="{key_id}",algorithm="rsa-sha256",headers="{sigheaders}",signature="{sig}"' # noqa: E501
logger.debug(f"signed request {sig_value=}")
r.headers["Signature"] = sig_value
yield r
k = Key(config.ID, f"{config.ID}#main-key")
k.load(KEY_PATH.read_text())
auth = HTTPXSigAuth(k)