Digest Authentication in aiohttp (Server & Client) Side

Digest Authentication is a secure method for protecting web resources in HTTP applications.

In this tutorial, you will learn how to implement Digest Authentication both on the server side and client side using aiohttp in Python.

You’ll learn how to manage authentication states, implement advanced features, and address security considerations.

 

 

Implement Digest Authentication Server-side

To handle Digest Authentication, you need to create a class that manages the authentication process.

import hashlib
import os
import time
from aiohttp import web
class DigestAuth:
  def __init__(self, realm, users):
      self.realm = realm
      self.users = users  # Dictionary of username:password

  def generate_nonce(self):
      return hashlib.md5(os.urandom(16)).hexdigest()

  def generate_opaque(self):
      return hashlib.md5(os.urandom(16)).hexdigest()

The DigestAuth class initializes with a realm and a dictionary of users. It includes methods to generate nonce and opaque values using MD5 hashing.

Generate nonce and opaque values

Nonce and opaque values are crucial for Digest Authentication. They ensure each request is unique and prevent replay attacks.

auth = DigestAuth("localhost", {"user": "password"})
nonce = auth.generate_nonce()
opaque = auth.generate_opaque()
print(f"Nonce: {nonce}, Opaque: {opaque}")

Output:

Nonce: 6d8b7aa01ce31e1a9c3c7f5527e0a07e, Opaque: df4106bd361fd9fe3c517a55989585cd

Nonce and opaque values are generated using random data to ensure they are unique for each session.

Handle authentication challenges

To challenge a client, you need to send a 401 response with suitable headers.

async def handle_request(request):
  auth_header = request.headers.get('Authorization', '')
  if not auth_header:
      return web.Response(status=401, headers={
          'WWW-Authenticate': f'Digest realm="{auth.realm}", nonce="{nonce}", opaque="{opaque}"'
      })
  return web.Response(text="Authenticated")
app = web.Application()
app.router.add_get('/', handle_request)
web.run_app(app)

The server responds with a 401 status and a WWW-Authenticate header if the Authorization header is missing and prompts the client to authenticate.

Validate client responses

Once the client responds, validate the response to ensure it matches the expected hash.

def validate_response(auth_header, method, uri):
  # Simplified validation logic
  return True
async def handle_request(request):
  auth_header = request.headers.get('Authorization', '')
  if not auth_header or not validate_response(auth_header, request.method, request.path):
      return web.Response(status=401, headers={
          'WWW-Authenticate': f'Digest realm="{auth.realm}", nonce="{nonce}", opaque="{opaque}"'
      })
  return web.Response(text="Authenticated")

The server checks the Authorization header and validates it. If invalid, it sends a 401 response again.

 

Client side Digest Authentication

To perform Digest Authentication on the client side, use aiohttp.ClientSession.

import asyncio
from aiohttp import ClientSession
async def fetch(url):
  async with ClientSession() as session:
      async with session.get(url) as response:
          return await response.text()
async def main():
  url = 'http://localhost:8080/'
  content = await fetch(url)
  print(content)
if __name__ == "__main__":
  asyncio.run(main())

The client sends a request to the server. If a 401 response is received, it will need to handle the challenge.

Handle authentication challenges

When the server challenges the client, extract the nonce and other details to respond correctly.

import asyncio
from aiohttp import ClientSession
async def fetch_with_auth(url, username, password):
    async with ClientSession() as session:
        async with session.get(url) as response:
            if response.status == 401:
                # Extract nonce and other details from response headers
                # Respond with correct Authorization header
                pass
            return await response.text()
async def main():
    url = "http://localhost:8080"  # Replace with your URL
    result = await fetch_with_auth(url, "user", "password")
    print(result)
asyncio.run(main())

The client checks for a 401 status and prepares to respond with the correct Authorization header.

Generate client responses

Generate the appropriate response hash using the nonce and other details.

import asyncio
from aiohttp import ClientSession
def generate_response_hash(username, password, realm, nonce, uri, method):
    # Simplified hash generation logic
    return "response_hash"
async def fetch_with_auth(url, username, password):
    async with ClientSession() as session:
        async with session.get(url) as response:
            if response.status == 401:
                # Extract realm and nonce from the WWW-Authenticate header
                www_authenticate = response.headers.get('WWW-Authenticate', '')
                # This is a simplified extraction; in practice, you should parse the header properly
                realm = "example_realm"  # Extracted from www_authenticate
                nonce = "example_nonce"  # Extracted from www_authenticate

                # Generate response hash
                auth_header = f'Digest username="{username}", response="{generate_response_hash(username, password, realm, nonce, url, "GET")}"'
                async with session.get(url, headers={'Authorization': auth_header}) as auth_response:
                    return await auth_response.text()
async def main():
    url = "http://localhost:8080"
    response_text = await fetch_with_auth(url, "user", "password")
    print(response_text)
asyncio.run(main())

The client generates a response hash and sends it in the Authorization header to authenticate successfully.

 

Caching Authentication Information

Caching authentication information can improve performance by reducing repeated calculations.

class AuthCache:
    def __init__(self):
        self.cache = {}
    def set(self, key, value, expiry=300):
        self.cache[key] = (value, time.time() + expiry)
    def get(self, key):
        if key in self.cache:
            value, expiry = self.cache[key]
            if time.time() < expiry:
                return value
        return None
auth_cache = AuthCache()

This AuthCache class allows you to store and retrieve authentication information with expiration times.

 

Nonce Counting (nc)

You can implement nonce counting to track request numbers:

class NonceCounter:
    def __init__(self):
        self.counters = {}
    def increment(self, nonce):
        if nonce not in self.counters:
            self.counters[nonce] = 1
        else:
            self.counters[nonce] += 1
        return self.counters[nonce]
nonce_counter = NonceCounter()
print(f"Nonce count: {nonce_counter.increment('nonce1')}")
print(f"Nonce count: {nonce_counter.increment('nonce1')}")

Output:

Nonce count: 1
Nonce count: 2

The NonceCounter class keeps track of how many times each nonce has been used.

 

Quality of Protection (qop) options

Implement Quality of Protection options:

def generate_response_with_qop(username, password, realm, nonce, nc, cnonce, qop, method, uri):
    ha1 = hashlib.md5(f"{username}:{realm}:{password}".encode()).hexdigest()
    ha2 = hashlib.md5(f"{method}:{uri}".encode()).hexdigest()
    if qop == 'auth':
        return hashlib.md5(f"{ha1}:{nonce}:{nc}:{cnonce}:{qop}:{ha2}".encode()).hexdigest()
    else:
        return hashlib.md5(f"{ha1}:{nonce}:{ha2}".encode()).hexdigest()
response = generate_response_with_qop("user1", "password123", "MyWebsite", "nonce1", "00000001", "cnonce1", "auth", "GET", "/")
print(f"Response with qop: {response}")

Output:

Response with qop: d0d6ecaeff13842c6f528f387a3b4961

This function generates a response that includes the Quality of Protection option.

 

Store and Compare Password Hashes

You must store and compare password hashes instead of plain text passwords:

import bcrypt
def hash_password(password):
    return bcrypt.hashpw(password.encode(), bcrypt.gensalt())
def verify_password(stored_hash, provided_password):
    return bcrypt.checkpw(provided_password.encode(), stored_hash)
stored_hash = hash_password("password123")
print(f"Password hash: {stored_hash}")
print(f"Password verification: {verify_password(stored_hash, 'password123')}")

Output:

Password hash: b'$2b$12$O8h.jTMUJtCFTpmuUVMXMeA5hlfV/kVaRdHbl/qoQV/qX5I487fcy'
Password verification: True

These functions use bcrypt to hash and verify passwords.