Functional one-time payments and tests

pyproject.toml

@@ -13,7 +13,8 @@ dependencies = [
     "httpx (>=0.28.1,<0.29.0)",
     "pydantic (>=2.10.6,<3.0.0)",
     "cryptography (>=45.0.4,<46.0.0)",
-    "http-message-signatures (>=0.6.1,<0.7.0)"
+    "http-message-signatures (>=0.6.1,<0.7.0)",
+    "http-sf (>=1.0.4,<1.1.0)"
 ]
 
 [build-system]

src/open_payments_sdk/gnap_utils/security.py

@@ -7,6 +7,7 @@
 from typing import Sequence
 from http_message_signatures import HTTPMessageSigner, algorithms
 import http_sfv
+from http_sf import ser
 from httpx import Request
 from open_payments_sdk.gnap_utils.hash import HashManager
 from open_payments_sdk.gnap_utils.http_signatures import OPKeyResolver, PatchedHTTPSignatureComponentResolver
@@ -49,6 +50,6 @@ def set_content_digest(self, request: Request) -> Request:
         """
         Compute Digest
         """
-        request.headers["Content-Digest"] = str(http_sfv.Dictionary({"sha-512": hashlib.sha512(request.content).digest()}))
+        request.headers["Content-Digest"] = ser({"sha-512": hashlib.sha512(request.content).digest()})
         return request