diff --git a/litellm/proxy/_experimental/mcp_server/openapi_oauth2_endpoints.py b/litellm/proxy/_experimental/mcp_server/openapi_oauth2_endpoints.py
index 1e8d7c138c1..b39093d465e 100644
--- a/litellm/proxy/_experimental/mcp_server/openapi_oauth2_endpoints.py
+++ b/litellm/proxy/_experimental/mcp_server/openapi_oauth2_endpoints.py
@@ -202,9 +202,15 @@ async def openapi_oauth2_connect(
             detail="Database is not configured. Cannot initiate OAuth2 flow.",
         )
 
-    user_id = user_api_key_dict.user_id or user_api_key_dict.api_key or ""
+    # Require an explicit user_id so that credentials are scoped to users, not API keys.
+    # Falling back to the raw api_key would allow multiple users sharing a key to
+    # silently share OAuth2 credentials and orphan them when the key is rotated.
+    user_id = user_api_key_dict.user_id or ""
     if not user_id:
-        raise HTTPException(status_code=400, detail="Cannot determine user identity from token")
+        raise HTTPException(
+            status_code=400,
+            detail="user_id is required for OAuth2 flow. Ensure your API key is tied to a user.",
+        )
 
     _purge_expired_states()
     if len(_pending_oauth2_states) >= _STATES_MAX_SIZE:
@@ -379,7 +385,7 @@ async def openapi_oauth2_callback(  # noqa: PLR0915
                 headers=token_headers,
                 timeout=30.0,
             )
-        response.raise_for_status()
+            response.raise_for_status()
     except httpx.HTTPStatusError as exc:
         verbose_proxy_logger.error(
             "openapi_oauth2_callback: token exchange HTTP error user=%s server=%s status=%s",
@@ -555,7 +561,8 @@ async def openapi_oauth2_status(
     if server is None:
         raise HTTPException(status_code=404, detail=f"MCP server '{server_id}' not found")
 
-    user_id = user_api_key_dict.user_id or user_api_key_dict.api_key or ""
+    # Use only user_id (not api_key) to avoid sharing credentials across users.
+    user_id = user_api_key_dict.user_id or ""
     server_name = server.server_name or server.name or server_id
 
     if prisma_client is None or not user_id:
diff --git a/litellm/proxy/_experimental/mcp_server/server.py b/litellm/proxy/_experimental/mcp_server/server.py
index 2f2f84fef4c..cdabc653f83 100644
--- a/litellm/proxy/_experimental/mcp_server/server.py
+++ b/litellm/proxy/_experimental/mcp_server/server.py
@@ -9,6 +9,7 @@ import json
 import time
 import traceback
 import uuid
+from collections import OrderedDict
 from datetime import datetime
 from typing import (
     Any,
@@ -67,7 +68,7 @@ from litellm.utils import Rules, client, function_setup
 # a brief 401 window (up to _BYOK_CRED_CACHE_TTL seconds) after a token expires at the
 # provider before the cache entry is evicted and a fresh DB lookup is made.  Mitigating
 # this (e.g. by storing and checking `expires_in`) is a future improvement.
-_byok_cred_cache: Dict[Tuple[str, str], Tuple[Optional[str], float]] = {}
+_byok_cred_cache: OrderedDict[Tuple[str, str], Tuple[Optional[str], float]] = OrderedDict()
 _BYOK_CRED_CACHE_TTL = 60  # seconds
 _BYOK_CRED_CACHE_MAX_SIZE = 4096  # cap to prevent unbounded growth
 
@@ -103,17 +104,19 @@ def _invalidate_byok_cred_cache(user_id: str, server_id: str) -> None:
 def _write_byok_cred_cache(
     user_id: str, server_id: str, credential: Optional[str]
 ) -> None:
-    """Write a credential value to the cache, evicting the oldest entry if at capacity.
+    """Write a credential value to the cache with LRU eviction.
 
-    Evicts the oldest-inserted entry (FIFO) rather than clearing all at once to
-    avoid a thundering-herd DB spike when the cache fills under load.
+    Uses OrderedDict.move_to_end() so that every write (new or update) moves
+    the entry to the most-recently-used position.  When at capacity, the
+    least-recently-used (oldest) entry at the front is evicted.
     """
     cache_key = (user_id, server_id)
-    # Only evict when the key is new — updates to existing entries don't grow the cache.
-    if cache_key not in _byok_cred_cache and len(_byok_cred_cache) >= _BYOK_CRED_CACHE_MAX_SIZE:
-        oldest_key = next(iter(_byok_cred_cache))
-        del _byok_cred_cache[oldest_key]
+    is_new = cache_key not in _byok_cred_cache
+    if is_new and len(_byok_cred_cache) >= _BYOK_CRED_CACHE_MAX_SIZE:
+        _byok_cred_cache.popitem(last=False)  # evict LRU (front of OrderedDict)
     _byok_cred_cache[cache_key] = (credential, time.monotonic())
+    if not is_new:
+        _byok_cred_cache.move_to_end(cache_key)  # promote to most-recently-used
 
 # Check if MCP is available
 # "mcp" requires python 3.10 or higher, but several litellm users use python 3.8