basic_ap/basic_ap.py

# This is a simple python flask implementation of 'How To Implement A Basic ActivityPub Server'
# https://blog.joinmastodon.org/2018/06/how-to-implement-a-basic-activitypub-server/
# © 2018 homebrewserver.club contributors

# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.

# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.

# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <https://www.gnu.org/licenses/>.

import flask
import os
import requests
import base64
import json

from flask import request
from flask import Response
from time import strftime, gmtime


from Crypto.Hash import SHA256
from Crypto.Signature import pkcs1_15
from Crypto.PublicKey import RSA

#
import logging
import http.client as http_client
http_client.HTTPConnection.debuglevel = 1

logging.basicConfig()
logging.getLogger().setLevel(logging.DEBUG)
requests_log = logging.getLogger("requests.packages.urllib3")
requests_log.setLevel(logging.DEBUG)
requests_log.propagate = True

#

#Config
DOMAIN = 'https://my-example.com'
USERNAME = 'alice'

def public_key():
    """
    Use commandline openssl to generate a public and private key
    """
    if not os.path.exists('public.pem'):
        os.system('openssl genrsa -out private.pem 2048')
        os.system('openssl rsa -in private.pem -outform PEM -pubout -out public.pem')
    else:
        public_key = open('public.pem').read() 
        public_key = public_key.replace('\n','\\n') #public key shouldn't contain verbatim linebreaks in json
        return public_key

public_key() #generate public_key on first launch

def build_signing_string(headers, header_values):
    return '\n'.join(map(lambda x: ': '.join([x.lower(), headers[x]]), header_values))

def messageContentDigest(messageBodyJsonStr: str) -> str:
    msg = messageBodyJsonStr.encode('utf-8')
    digestStr = SHA256.new(msg).digest()
    return base64.b64encode(digestStr).decode('utf-8')



def sign_header(private_key, keyID, host, messageBodyJsonStr):
    """
    Sign HTTP headers 
    """
    date = strftime("%a, %d %b %Y %H:%M:%S %Z", gmtime()) #RFC1123 Time format

    #Based on https://code.freedombone.net/bashrc/epicyon/src/main/httpsig.py
    keyfile = open(private_key,'rb').read()
    secret = RSA.import_key(keyfile) 

    bodyDigest = messageContentDigest(messageBodyJsonStr)
    contentLength = len(messageBodyJsonStr)
    print(contentLength)
    
    path = '/inbox'

    headers = {
            '(request-target)': f'post {path}',
            'host': host,
            'date': date,
            'digest': f'SHA-256={bodyDigest}',
            'content-type': 'application/json',
            'content-length': str(contentLength)
        }


    signedHeaderKeys = headers.keys()
    signedHeaderText = ''

    for headerKey in signedHeaderKeys:
        signedHeaderText += f'{headerKey}: {headers[headerKey]}\n'

    signedHeaderText = signedHeaderText.strip()
    headerDigest = SHA256.new(signedHeaderText.encode('ascii'))

    # Sign the digest
    rawSignature = pkcs1_15.new(secret).sign(headerDigest)
    signature = base64.b64encode(rawSignature).decode('ascii')

    # Put it into a valid HTTP signature format
    signatureDict = {
        'keyId': keyID,
        'algorithm': 'rsa-sha256',
        'headers': ' '.join(signedHeaderKeys),
        'signature': signature
    }
    signatureHeader = ','.join(
        [f'{k}="{v}"' for k, v in signatureDict.items()])
    

    headers['signature'] = signatureHeader

    return headers




#Flask
app = flask.Flask(__name__)

@app.route('/')
def index():
    return 'It works! Now try to look for a user@my-example.com via the mastodon interface'

@app.route('/.well-known/webfinger')
def finger():
    """
    Respond to webfinger queries (GET /.well-known/webfinger?resource=acct:alice@my-example.com) with a json object pointing to the actor
    see templates/webfinger.json

    """
    if request.args.get('resource'):
        query = request.args.get('resource')

        actor = query.split(':')[1].split('@')[0] # from 'acct:alice@my-example.com' to 'alice'

        json = flask.render_template('webfinger.json', query=query, actor=actor, domain=DOMAIN) # render our ActivityPub answer

        return Response(response=json, status=200,  mimetype="application/json") # return that answer as a json object
        
@app.route('/users/<actor>')
def profile(actor):
    """
    Return an Actor object 
    see templates/actor.json
    """
    json = flask.render_template('actor.json', preferred_username=USERNAME, actor=actor, domain=DOMAIN, public_key=public_key()) # render our ActivityPub answer
    return Response(response=json, status=200,  mimetype="application/json") # return that answer as a json object


@app.route('/post/', methods=['POST','GET'])
def post():
    date = strftime("%a, %d %b %Y %H:%M:%S GMT", gmtime())

    json_message=json.loads(flask.render_template('create.json',
        domain=DOMAIN,public_key=public_key(),actor=USERNAME,host='DOMAIN', date=date))
    
    signed_headers = sign_header('private.pem', DOMAIN+'/users/'+USERNAME+'#main-key','https://post.lurk.org', json.dumps(json_message))

    r = requests.post('https://post.lurk.org/inbox', json=json_message, headers=signed_headers)

    a = (r.status_code, r.text, r.headers)
    a = str(a)
    
    return a

if __name__ == '__main__':
    app.debug =True
    app.run()