89 lines
3 KiB
Python
89 lines
3 KiB
Python
"""Implements HTTP signature for Flask requests.
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Mastodon instances won't accept requests that are not signed using this scheme.
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"""
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from datetime import datetime
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from urllib.parse import urlparse
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from typing import Any, Dict
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import base64
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import hashlib
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import logging
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from flask import request
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from requests.auth import AuthBase
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from Crypto.Signature import PKCS1_v1_5
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from Crypto.Hash import SHA256
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logger = logging.getLogger(__name__)
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def _build_signed_string(signed_headers: str, method: str, path: str, headers: Any, body_digest: str) -> str:
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out = []
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for signed_header in signed_headers.split(' '):
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if signed_header == '(request-target)':
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out.append('(request-target): '+method.lower()+' '+path)
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elif signed_header == 'digest':
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out.append('digest: '+body_digest)
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else:
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out.append(signed_header+': '+headers[signed_header])
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return '\n'.join(out)
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def _parse_sig_header(val: str) -> Dict[str, str]:
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out = {}
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for data in val.split(','):
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k, v = data.split('=', 1)
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out[k] = v[1:len(v)-1]
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return out
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def _verify_h(signed_string, signature, pubkey):
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signer = PKCS1_v1_5.new(pubkey)
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digest = SHA256.new()
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digest.update(signed_string.encode('utf-8'))
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return signer.verify(digest, signature)
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def _body_digest() -> str:
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h = hashlib.new('sha256')
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h.update(request.data)
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return 'SHA-256='+base64.b64encode(h.digest()).decode('utf-8')
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def verify_request(actor_service) -> bool:
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hsig = _parse_sig_header(request.headers.get('Signature'))
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logger.debug(f'hsig={hsig}')
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signed_string = _build_signed_string(hsig['headers'], request.method, request.path, request.headers, _body_digest())
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_, rk = actor_service.get_public_key(hsig['keyId'])
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return _verify_h(signed_string, base64.b64decode(hsig['signature']), rk)
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class HTTPSigAuth(AuthBase):
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def __init__(self, keyid, privkey):
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self.keyid = keyid
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self.privkey = privkey
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def __call__(self, r):
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logger.info(f'keyid={self.keyid}')
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host = urlparse(r.url).netloc
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bh = hashlib.new('sha256')
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bh.update(r.body.encode('utf-8'))
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bodydigest = 'SHA-256='+base64.b64encode(bh.digest()).decode('utf-8')
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date = datetime.utcnow().strftime('%a, %d %b %Y %H:%M:%S GMT')
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r.headers.update({'Digest': bodydigest, 'Date': date})
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r.headers.update({'Host': host})
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sigheaders = '(request-target) user-agent host date digest content-type'
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to_be_signed = _build_signed_string(sigheaders, r.method, r.path_url, r.headers, bodydigest)
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signer = PKCS1_v1_5.new(self.privkey)
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digest = SHA256.new()
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digest.update(to_be_signed.encode('utf-8'))
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sig = base64.b64encode(signer.sign(digest))
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sig = sig.decode('utf-8')
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headers = {
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'Signature': f'keyId="{self.keyid}",algorithm="rsa-sha256",headers="{sigheaders}",signature="{sig}"'
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}
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logger.info(f'signed request headers={headers}')
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r.headers.update(headers)
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return r
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