feat/add digest calculate

app/httpsig.py

@@ -0,0 +1,26 @@
+#!/usr/bin/env python3
+import base64
+from typing import Literal, TypedDict, cast, Any
+
+from Crypto.Hash import SHA256
+from Crypto.Signature import PKCS1_v1_5
+
+class HttpSignature:
+    """
+    calculation and verification of HTTP signatures
+    """
+
+    @classmethod
+    def calculation_digest(cls,
+                               body: bytes,
+                               algorithm="sha-256")-> str :
+        """
+        Calculates the digest header value for a given HTTP body
+        """
+        if "sha-256" == algorithm:
+            h = SHA256.new()
+            h.update(body)
+            return "SHA-256=" + \
+                base64.b64encode(h.digest()).decode("utf-8")
+        else:
+            raise ValueError(f"Not support algorithm {algorithm}")