Generate a Mock Presigned URL in Python with HMAC

import hashlib
import hmac
import time
import base64

def generate_presigned_url_mock(secret_key, bucket, object_key, expires_in=3600):
    # Build the canonical request string (simplified AWS SigV4 style)
    timestamp = str(int(time.time()))
    expiry = str(int(time.time()) + expires_in)
    payload = f"GET\n/{bucket}/{object_key}\n{timestamp}\n{expiry}"
    
    # Generate HMAC-SHA256 signature
    signature = hmac.new(
        secret_key.encode(),
        payload.encode(),
        hashlib.sha256
    ).hexdigest()
    
    # Encode and format URL
    base_url = f"https://{bucket}.s3.amazonaws.com/{object_key}"
    query_params = {
        "X-Amz-Algorithm": "AWS4-HMAC-SHA256",
        "X-Amz-Credential": "mock-credentials",
        "X-Amz-Date": timestamp,
        "X-Amz-Expires": str(expires_in),
        "X-Amz-Signature": signature
    }
    
    query_string = "&".join(f"{k}={v}" for k, v in query_params.items())
    return f"{base_url}?{query_string}"

if __name__ == "__main__":
    secret_key = "my-secret-key-123"
    bucket = "my-demo-bucket"
    object_key = "photos/vacation.jpg"
    
    url = generate_presigned_url_mock(secret_key, bucket, object_key, expires_in=3600)
    print("Generated Presigned URL:")
    print(url)
    
    # Verify signature reproducibility
    url2 = generate_presigned_url_mock(secret_key, bucket, object_key, expires_in=3600)
    sig1 = url2.split("X-Amz-Signature=")[1][:64]
    sig2 = url.split("X-Amz-Signature=")[1][:64]
    print(f"\nSignature reproducible: {sig1 == sig2}")