feat: Check if token is a JWT (#529)

Author: juancarlospaco

postgrest/base_client.py

@@ -5,7 +5,7 @@
 
 from httpx import BasicAuth, Timeout
 
-from .utils import AsyncClient, SyncClient, is_http_url
+from .utils import AsyncClient, SyncClient, is_http_url, is_valid_jwt
 
 
 class BasePostgrestClient(ABC):
@@ -58,6 +58,8 @@ def auth(
             Bearer token is preferred if both ones are provided.
         """
         if token:
+            if not is_valid_jwt(token):
+                ValueError("token must be a valid JWT authorization token")
             self.session.headers["Authorization"] = f"Bearer {token}"
         elif username:
             self.session.auth = BasicAuth(username, password)

postgrest/utils.py

@@ -1,11 +1,14 @@
 from __future__ import annotations
 
+import re
 from typing import Any, Type, TypeVar, cast, get_origin
 from urllib.parse import urlparse
 
 from httpx import AsyncClient  # noqa: F401
 from httpx import Client as BaseClient  # noqa: F401
 
+BASE64URL_REGEX = r"^([a-z0-9_-]{4})*($|[a-z0-9_-]{3}$|[a-z0-9_-]{2}$)$"
+
 
 class SyncClient(BaseClient):
     def aclose(self) -> None:
@@ -40,3 +43,26 @@ def get_origin_and_cast(typ: type[type[_T]]) -> type[_T]:
 
 def is_http_url(url: str) -> bool:
     return urlparse(url).scheme in {"https", "http"}
+
+
+def is_valid_jwt(value: str) -> bool:
+    """Checks if value looks like a JWT, does not do any extra parsing."""
+    if not isinstance(value, str):
+        return False
+
+    # Remove trailing whitespaces if any.
+    value = value.strip()
+
+    # Remove "Bearer " prefix if any.
+    if value.startswith("Bearer "):
+        value = value[7:]
+
+    # Valid JWT must have 2 dots (Header.Paylod.Signature)
+    if value.count(".") != 2:
+        return False
+
+    for part in value.split("."):
+        if not re.search(BASE64URL_REGEX, part, re.IGNORECASE):
+            return False
+
+    return True