usigv4

minimal aws signature version 4 implementation for micropython/embedded use.

why

while the sigv4 algorithm is very straightforward, this implementation tries to optimize it for microcontrollers and the like by making most of the string manipulation in-place.

what it does

• signs http requests per aws sigv4 spec
• zero dependencies beyond stdlib and micropython-lib
• micropython compatible (no datetime, string ops in-place)

todo (patches are welcome):

• support querystring signing
• support multiple headers
• support presigned urls

usage

from usigv4 import sign_request_headers
import requests

headers = sign_request_headers(
    method="POST",
    host="lambda.us-west-2.amazonaws.com",
    path="/2025-03-31/functions/my-func/invocations",
    body=b'{"hello": "world"}', # byte representation of header data
    ak="AKIA...",
    sk="wJal...",
    region="us-west-2",
    service="lambda"
)

resp = requests.post(
    "https://lambda.us-west-2.amazonaws.com/2025-03-31/functions/my-func/invocations",
    headers=headers, # signed headers
    data=b'{"hello": "world"}' # must be identical to headers' body
)

caveats

• body must be bytes for hashing
• only signs host header (sufficient for some aws apis)
• hardcoded json content-type
• depends on time.gmtime()'s accuracy