Fix the problem where a wrong realm is found in www-authenticate (#88)

* Fix the problem where a wrong realm is found in www-authenticate

The token cache returned an invalid token for the container registry
and when using that token on the first request we got an incorrect
realm in the www-authenticate header.
If that happens we will now invalidate the cache and do a HEAD
request without a token to get a proper www-authenticate.

Author: t-persson

python/src/etos_api/library/docker.py

@@ -16,6 +16,7 @@
 """Docker operations for the ETOS API."""
 import time
 import logging
+from typing import Optional, Mapping
 from threading import Lock
 import aiohttp
 
@@ -33,12 +34,14 @@ class Docker:
     """
 
     logger = logging.getLogger(__name__)
+    # The amount of time in seconds before the token expires where we should recreate it.
+    token_expire_modifier = 30
     # In-memory database for stored authorization tokens.
     # This dictionary shares memory with all instances of `Docker`, by design.
     tokens = {}
     lock = Lock()
 
-    def token(self, manifest_url: str) -> str:
+    def token(self, manifest_url: str) -> Optional[str]:
         """Get a stored token, removing it if expired.
 
         :param manifest_url: URL the token has been stored for.
@@ -54,7 +57,7 @@ def token(self, manifest_url: str) -> str:
             return token.get("token")
 
     async def head(
-        self, session: aiohttp.ClientSession, url: str, token: str = None
+        self, session: aiohttp.ClientSession, url: str, token: Optional[str] = None
     ) -> aiohttp.ClientResponse:
         """Make a HEAD request to a URL, adding token to headers if supplied.
 
@@ -70,36 +73,78 @@ async def head(
         async with session.head(url, headers=headers) as response:
             return response
 
-    async def authorize(
-        self, session: aiohttp.ClientSession, response: aiohttp.ClientResponse
-    ) -> str:
-        """Get a token from an unauthorized request to image repository.
+    async def get_token_from_container_registry(
+        self, session: aiohttp.ClientSession, realm: str, parameters: dict
+    ) -> dict:
+        """Get a token from an unauthorized request to container repository.
 
         :param session: Client HTTP session to use for HTTP request.
-        :param response: HTTP response to get headers from.
+        :param realm: The realm to authorize against.
+        :param parameters: Parameters to use for the authorization request.
         :return: Response JSON from authorization request.
         """
-        www_auth_header = response.headers.get("www-authenticate")
-        challenge = www_auth_header.replace("Bearer ", "")
-        parts = challenge.split(",")
+        async with session.get(realm, params=parameters) as response:
+            response.raise_for_status()
+            return await response.json()
 
-        url = None
-        query = {}
-        for part in parts:
-            key, value = part.split("=")
-            if key == "realm":
-                url = value.strip('"')
-            else:
-                query[key] = value.strip('"')
+    async def authorize(
+        self, session: aiohttp.ClientSession, response: aiohttp.ClientResponse, manifest_url: str
+    ) -> str:
+        """Authorize against container registry.
 
+        :param session: Client HTTP session to use for HTTP request.
+        :param response: Response from a previous request to parse headers from.
+        :param manifest_url: Manifest URL to query should a new auth request be needed.
+        :return: A token retrieved from container registry.
+        """
+        parameters = await self.parse_headers(response.headers)
+        url = parameters.get("realm")
         if not isinstance(url, str) or not (
             url.startswith("http://") or url.startswith("https://")
         ):
-            raise ValueError(f"No realm URL found in www-authenticate header: {www_auth_header}")
+            self.logger.warning("No realm in original request, retrying without a token")
+            with self.lock:
+                try:
+                    del self.tokens[manifest_url]
+                except KeyError:
+                    pass
+            response = await self.head(session, manifest_url)
+            parameters = await self.parse_headers(response.headers)
+            url = parameters.get("realm")
+            if not isinstance(url, str) or not (
+                url.startswith("http://") or url.startswith("https://")
+            ):
+                raise ValueError(
+                    f"No realm URL found in www-authenticate header: {response.headers}"
+                )
+        url = parameters.pop("realm")
+        response_json = await self.get_token_from_container_registry(session, url, parameters)
+        with self.lock:
+            self.tokens[manifest_url] = {
+                "token": response_json.get("token"),
+                "expire": time.time()
+                + response_json.get("expires_in", 0.0)
+                - self.token_expire_modifier,
+            }
+        return ""
+
+    async def parse_headers(self, headers: Mapping) -> dict:
+        """Parse the www-authenticate header and convert it to a dict.
+
+        :param headers: Headers to parse.
+        :return: Dictionary of the keys in the www-authenticate header.
+        """
+        www_auth_header = headers.get("www-authenticate")
+        if www_auth_header is None:
+            return {}
+        challenge = www_auth_header.replace("Bearer ", "")
+        parts = challenge.split(",")
 
-        async with session.get(url, params=query) as response:
-            response.raise_for_status()
-            return await response.json()
+        parameters = {}
+        for part in parts:
+            key, value = part.split("=")
+            parameters[key] = value.strip('"')
+        return parameters
 
     def tag(self, base: str) -> tuple[str, str]:
         """Figure out tag from a container image name.
@@ -149,7 +194,7 @@ def repository(self, repo: str) -> tuple[str, str]:
             registry = DEFAULT_REGISTRY
         return registry, repo
 
-    async def digest(self, name: str) -> str:
+    async def digest(self, name: str) -> Optional[str]:
         """Get a sha256 digest from an image in an image repository.
 
         :param name: The name of the container image.
@@ -167,13 +212,8 @@ async def digest(self, name: str) -> str:
             try:
                 if response.status == 401 and "www-authenticate" in response.headers:
                     self.logger.info("Generate a new authorization token for %r", manifest_url)
-                    response_json = await self.authorize(session, response)
-                    with self.lock:
-                        self.tokens[manifest_url] = {
-                            "token": response_json.get("token"),
-                            "expire": time.time() + response_json.get("expires_in"),
-                        }
-                    response = await self.head(session, manifest_url, self.token(manifest_url))
+                    token = await self.authorize(session, response, manifest_url)
+                    response = await self.head(session, manifest_url, token)
                 digest = response.headers.get("Docker-Content-Digest")
             except aiohttp.ClientResponseError as exception:
                 self.logger.error("Error getting container image %r", exception)