add auth using bearer tokens

These tokens are used to gain global admin rights, or to gain more
resource specific capabilities, like adding users to a group.

unwind/web.py

@@ -8,8 +8,8 @@ from starlette.authentication import (
     AuthCredentials,
     AuthenticationBackend,
     AuthenticationError,
+    BaseUser,
     SimpleUser,
-    UnauthenticatedUser,
     requires,
 )
 from starlette.exceptions import HTTPException
@@ -28,23 +28,40 @@ from .utils import b64encode, phc_compare, phc_scrypt
 log = logging.getLogger(__name__)
 
 
-class BasicAuthBackend(AuthenticationBackend):
+class BearingUser(BaseUser):
+    def __init__(self, token):
+        self.token = token
+
+
+class BearerAuthBackend(AuthenticationBackend):
+    def __init__(self, credentials: dict[str, str]):
+        self.admin_tokens = {v: k for k, v in credentials.items()}
+
     async def authenticate(self, request):
         if "Authorization" not in request.headers:
             return
 
         auth = request.headers["Authorization"]
         try:
-            scheme, credentials = auth.split()
-            if scheme.lower() != "basic":
-                return
-            decoded = base64.b64decode(credentials).decode("ascii")
-        except (ValueError, UnicodeDecodeError, binascii.Error) as exc:
-            raise AuthenticationError("Invalid basic auth credentials")
+            scheme, token = auth.split()
+        except ValueError:
+            raise AuthenticationError("Invalid auth credentials")
 
-        username, _, password = decoded.partition(":")
-        # TODO: You'd want to verify the username and password here.
-        return AuthCredentials(["authenticated"]), SimpleUser(username)
+        if scheme.lower() != "bearer":
+            return
+
+        roles = []
+
+        is_admin = token in self.admin_tokens
+
+        if is_admin:
+            user = SimpleUser(self.admin_tokens[token])
+            roles.append("admin")
+
+        else:
+            user = BearingUser(token)
+
+        return AuthCredentials(["authenticated", *roles]), user
 
 
 def imdb_url(imdb_id: str):
@@ -210,7 +227,7 @@ async def add_group(request):
     )
 
 
-@requires(["authenticated", "admin"])
+@requires(["authenticated"])
 async def add_user_to_group(request):
     group_id = as_ulid(request.path_params["group_id"])
     group = await db.get(Group, id=str(group_id))
@@ -251,6 +268,14 @@ async def add_user_to_group(request):
     return JSONResponse(asplain(group))
 
 
+async def http_exception(request, exc):
+    return JSONResponse({"error": exc.detail}, status_code=exc.status_code)
+
+
+def auth_error(request, err):
+    return unauthorized(str(err))
+
+
 def create_app():
     if config.loglevel == "DEBUG":
         logging.basicConfig(
@@ -285,6 +310,11 @@ def create_app():
         ],
         middleware=[
             Middleware(ResponseTimeMiddleware, header_name="Unwind-Elapsed"),
-            Middleware(AuthenticationMiddleware, backend=BasicAuthBackend()),
+            Middleware(
+                AuthenticationMiddleware,
+                backend=BearerAuthBackend(config.api_credentials),
+                on_error=auth_error,
+            ),
         ],
+        exception_handlers={HTTPException: http_exception},
     )