#!/usr/bin/python3.4
"""Docker Auth Service in Python

PoC for Docker Registry v2 authentication via central service

https://docs.docker.com/registry/spec/auth/token/
https://docs.docker.com/registry/spec/auth/jwt/

Authors:
    Christian Heimes <cheimes@redhat.com>

Copyright (C) 2015 Red Hat, Inc.
All rights reserved.
"""
from http.server import HTTPServer, BaseHTTPRequestHandler
import urllib.parse
import time
import os
import base64
import json
import struct
import pprint

from jwcrypto.common import base64url_encode
from jwcrypto.jwk import JWK
from jwcrypto.jws import JWS
from jwcrypto.jwt import JWT

from cryptography.hazmat.backends import default_backend
from cryptography.x509 import load_pem_x509_certificate
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives.serialization import Encoding
from cryptography.hazmat.primitives.serialization import PublicFormat

ISSUER = "C=XX, L=Default City, O=Default Company Ltd, CN=auth.example.org"


def n2b64(n, endian='big'):
    """Arbitrary number to base64
    """
    b = n.to_bytes((n.bit_length() + 7) // 8, endian)
    return base64.urlsafe_b64encode(b).rstrip(b'=').decode('ascii')

def private_key(filename, kid, password=None):
    """Get JWK from private key PEM file
    """
    with open(filename, 'rb') as f:
        data = f.read()
    pkey = default_backend().load_pem_private_key(data, password)
    priv = pkey.private_numbers()
    pub = priv.public_numbers
    return JWK(
        kty='RSA',
        kid=kid,
        use='sig',
        n=n2b64(pub.n),
        e=n2b64(pub.e),
        d=n2b64(priv.d),
        p=n2b64(priv.p),
        q=n2b64(priv.q),
        dp=n2b64(priv.dmp1),
        dq=n2b64(priv.dmq1),
        qi=n2b64(priv.iqmp),
    )

def get_fingerprint(pemfile):
    """docker/libtrust compatible SPKI fingerprint

    https://github.com/docker/libtrust/blob/9cbd2a1374f46905c68a4eb3694a130610adc62a/util.go#L194
    keyIDFromCryptoKey
    """
    with open(pemfile, 'rb') as f:
        data = f.read()
    x509 = load_pem_x509_certificate(data, default_backend())
    pubkey = x509.public_key()
    public_bytes = pubkey.public_bytes(
        Encoding.DER,
        PublicFormat.SubjectPublicKeyInfo)
    digest = hashes.Hash(hashes.SHA256(), backend=default_backend())
    digest.update(public_bytes)
    fingerprint = digest.finalize()
    # strip of last two bytes
    fingerprint = fingerprint[:30]
    # base32 encode and add ':' every four chars
    fb32 = base64.b32encode(fingerprint).decode('ascii').rstrip('=')
    result = []
    for i, c in enumerate(fb32):
        result.append(c)
        if i % 4 == 3 and i != len(fb32) - 1:
            result.append(':')
    return ''.join(result)


def bearer_token(claims):
    kid = get_fingerprint('ssl/server.pem')
    jwk = private_key('ssl/server.key', kid)

    header = {
        "typ": "JWT",
        "alg": 'RS256',
        "kid": kid
    }

    token = JWT(header, claims)
    token.make_signed_token(key)
    return token.serialize()


class ClaimSet:
    def __init__(self, issuer, subject, audience):
        now = int(time.time())
        self.claims = {
            'access': []
            'aud': audience,
            'exp': now + 600
            'jti': base64url_encode(os.urandom(15))
            'iat': now,
            'iss': issuer,
            'nbf': now,
            'sub': subject,
        }

    def add_access(self, typ, name, actions):
        self.claims['access'].append(dict(
            type=typ,
            name=name,
            actions=actions,
        ))

    def __repr__(self):
        return "<%s %r>" % (type(self).__name__,
                            json.dumps(self.claims)


class DockerAuthHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        parts = urllib.parse.urlsplit(self.path)
        qs = urllib.parse.parse_qs(parts.query)
        if 0:
            pprint.pprint([vars(self), dict(self.headers), parts, qs])

        subject = qs.get('account', [''])[0]
        audience = qs.get('service', [''])[0]
        scopes = qs.get('scope', [])
        claimset = ClaimSet(ISSUER, subject, audience)
        for scope in scopes:
            typ, name, actions = scope.split(':')
            actions = list(a.strip() for a in actions.split(','))
            claimset.add_access(typ, name, actions)
        print(qs, claim)
        token = bearer_token(claimset.claims)
        token = b'{"token":"' + token + b'"}'

        self.send_response(200)
        self.send_header("Content-type", 'application/json')
        self.send_header("Content-Length", str(len(token)))
        self.end_headers()
        self.wfile.write(token)


def main():
    server_address = ('localhost', 5001)
    httpd = HTTPServer(server_address, DockerAuthHandler)
    httpd.serve_forever()

def test():
    kid = get_fingerprint('ssl/server.pem')
    jwk = private_key('ssl/server.key', kid)
    jws = JWS(b'data')
    jws.add_signature(jwk, alg="RS256")
    print(jws.serialize())
    bearer_token(ClaimSet('iss', 'subject', 'audience'))

if __name__ == '__main__':
    main()