import hmac
from datetime import datetime
from hashlib import sha256
import requests
[docs]class SigV4Auth:
[docs] def __init__(self, access_key, secret_key, session_token=None, region="us-east-1"):
self.access_key = access_key
self.secret_key = secret_key
self.session_token = session_token
self.region = region
[docs] def add_auth(self, request):
timestamp = datetime.utcnow().strftime("%Y%m%dT%H%M%SZ")
request.headers["X-Amz-Date"] = timestamp
if self.session_token:
request.headers["X-Amz-Security-Token"] = self.session_token
# https://docs.aws.amazon.com/general/latest/gr/sigv4-create-canonical-request.html
canonical_headers = "".join(
f"{k.lower()}:{request.headers[k]}\n" for k in sorted(request.headers)
)
signed_headers = ";".join(k.lower() for k in sorted(request.headers))
payload_hash = sha256(request.body.encode("utf-8")).hexdigest()
canonical_request = "\n".join(
[request.method, "/", "", canonical_headers, signed_headers, payload_hash]
)
# https://docs.aws.amazon.com/general/latest/gr/sigv4-create-string-to-sign.html
algorithm = "AWS4-HMAC-SHA256"
credential_scope = "/".join(
[timestamp[0:8], self.region, "sts", "aws4_request"]
)
canonical_request_hash = sha256(canonical_request.encode("utf-8")).hexdigest()
string_to_sign = "\n".join(
[algorithm, timestamp, credential_scope, canonical_request_hash]
)
# https://docs.aws.amazon.com/general/latest/gr/sigv4-calculate-signature.html
key = f"AWS4{self.secret_key}".encode()
key = hmac.new(key, timestamp[0:8].encode("utf-8"), sha256).digest()
key = hmac.new(key, self.region.encode("utf-8"), sha256).digest()
key = hmac.new(key, b"sts", sha256).digest()
key = hmac.new(key, b"aws4_request", sha256).digest()
signature = hmac.new(key, string_to_sign.encode("utf-8"), sha256).hexdigest()
# https://docs.aws.amazon.com/general/latest/gr/sigv4-add-signature-to-request.html
authorization = "{} Credential={}/{}, SignedHeaders={}, Signature={}".format(
algorithm, self.access_key, credential_scope, signed_headers, signature
)
request.headers["Authorization"] = authorization
[docs]def generate_sigv4_auth_request(header_value=None):
"""Helper function to prepare a AWS API request to subsequently generate a "AWS Signature Version 4" header.
:param header_value: Vault allows you to require an additional header, X-Vault-AWS-IAM-Server-ID, to be present
to mitigate against different types of replay attacks. Depending on the configuration of the AWS auth
backend, providing a argument to this optional parameter may be required.
:type header_value: str
:return: A PreparedRequest instance, optionally containing the provided header value under a
'X-Vault-AWS-IAM-Server-ID' header name pointed to AWS's simple token service with action "GetCallerIdentity"
:rtype: requests.PreparedRequest
"""
request = requests.Request(
method="POST",
url="https://sts.amazonaws.com/",
headers={
"Content-Type": "application/x-www-form-urlencoded; charset=utf-8",
"Host": "sts.amazonaws.com",
},
data="Action=GetCallerIdentity&Version=2011-06-15",
)
if header_value:
request.headers["X-Vault-AWS-IAM-Server-ID"] = header_value
prepared_request = request.prepare()
return prepared_request