diff --git a/app/indieauth.py b/app/indieauth.py
index 57640b5..7e657ea 100644
--- a/app/indieauth.py
+++ b/app/indieauth.py
@@ -10,6 +10,8 @@ from fastapi import Form
 from fastapi import HTTPException
 from fastapi import Request
 from fastapi.responses import JSONResponse
+from fastapi.security import HTTPBasic
+from fastapi.security import HTTPBasicCredentials
 from loguru import logger
 from pydantic import BaseModel
 from sqlalchemy import select
@@ -26,6 +28,8 @@ from app.redirect import redirect
 from app.utils import indieauth
 from app.utils.datetime import now
 
+basic_auth = HTTPBasic()
+
 router = APIRouter()
 
 
@@ -496,19 +500,49 @@ async def indieauth_revocation_endpoint(
 @router.post("/token_introspection")
 async def oauth_introspection_endpoint(
     request: Request,
-    access_token_info: AccessTokenInfo = Depends(enforce_access_token),
+    credentials: HTTPBasicCredentials = Depends(basic_auth),
+    db_session: AsyncSession = Depends(get_db_session),
     token: str = Form(),
 ) -> JSONResponse:
-    # Ensure the requested token is the same as bearer token
-    if token != access_token_info.access_token:
-        raise HTTPException(status_code=401, detail="access token required")
+    registered_client = (
+        await db_session.scalars(
+            select(models.OAuthClient).where(
+                models.OAuthClient.client_id == credentials.username,
+                models.OAuthClient.client_secret == credentials.password,
+            )
+        )
+    ).one_or_none()
+    if not registered_client:
+        raise HTTPException(status_code=401, detail="unauthenticated")
+
+    access_token = (
+        await db_session.scalars(
+            select(models.IndieAuthAccessToken)
+            .where(models.IndieAuthAccessToken.access_token == token)
+            .join(
+                models.IndieAuthAuthorizationRequest,
+                models.IndieAuthAccessToken.indieauth_authorization_request_id
+                == models.IndieAuthAuthorizationRequest.id,
+            )
+            .where(
+                models.IndieAuthAuthorizationRequest.client_id == credentials.username
+            )
+        )
+    ).one_or_none()
+    if not access_token:
+        return JSONResponse(content={"active": False})
 
     return JSONResponse(
         content={
             "active": True,
-            "client_id": access_token_info.client_id,
-            "scope": " ".join(access_token_info.scopes),
-            "exp": access_token_info.exp,
+            "client_id": credentials.username,
+            "scope": access_token.scope,
+            "exp": int(
+                (
+                    access_token.created_at.replace(tzinfo=timezone.utc)
+                    + timedelta(seconds=access_token.expires_in)
+                ).timestamp()
+            ),
         },
         status_code=200,
     )