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Why prefer stateless services and how do you handle sessions?

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01

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Explain statelessness.

statelesssessions
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04

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Stateless signed session token
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import hmac, hashlib, base64

SECRET = b"server-secret"     # shared by every instance

def issue(user_id):
    payload = ("user=" + str(user_id)).encode()
    sig = hmac.new(SECRET, payload, hashlib.sha256).hexdigest()[:12]
    return base64.urlsafe_b64encode(payload).decode() + "." + sig

def verify(token):
    raw, sig = token.split(".")
    payload = base64.urlsafe_b64decode(raw)
    expected = hmac.new(SECRET, payload, hashlib.sha256).hexdigest()[:12]
    return payload.decode() if hmac.compare_digest(sig, expected) else None

t = issue(42)
print("token   :", t)
print("verify  :", verify(t))            # ANY stateless instance can validate it
print("tampered:", verify(t[:-1] + "x")) # None -> rejected
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