docs(mcp): add token validation doc with screenshot and expected behavior table

docs/my-website/docs/mcp_token_validation.md

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+# MCP Token Validation
+
+Enforce that per-user OAuth tokens belong to your corporate workspace before LiteLLM stores them.
+
+**Use case:** Your company uses Slack. You want to ensure employees can only connect their `@yourco.com` Slack account — not a personal one. Configure `token_validation` rules on the MCP server, and LiteLLM rejects any token whose claims don't match.
+
+## How it works
+
+When a user completes OAuth and submits their token via `POST /server/{id}/oauth-user-credential`, LiteLLM checks the `token_response_metadata` fields against the `token_validation` rules you've configured. If any field is missing or doesn't match, the request is rejected with a `403` before the credential is stored.
+
+## Configuration
+
+### Via the UI
+
+Open **MCP Servers → Add New MCP Server**, set auth type to **OAuth**, and scroll to **Required Token Claims**:
+
+![Token claims builder](/img/mcp_token_validation.png)
+
+Click a quick-add chip (Slack enterprise, Jira cloud, GitHub Enterprise) or type your own key. Fill in the required value.
+
+### Via API
+
+```bash
+curl -X POST https://your-proxy/v1/mcp/server \
+  -H "Authorization: Bearer $LITELLM_MASTER_KEY" \
+  -H "Content-Type: application/json" \
+  -d '{
+    "name": "slack-corp",
+    "url": "https://slack.com/api/mcp",
+    "transport": "http",
+    "auth_type": "oauth2",
+    "token_validation": {
+      "enterprise_id": "E04COREWEAVE"
+    }
+  }'
+```
+
+### Via config.yaml
+
+```yaml title="config.yaml"
+mcp_servers:
+  slack_corp:
+    url: "https://slack.com/api/mcp"
+    auth_type: oauth2
+    token_validation:
+      enterprise_id: "E04COREWEAVE"
+```
+
+## Expected behavior
+
+When a user submits their OAuth credential:
+
+| Scenario | Result |
+|----------|--------|
+| `token_response_metadata: {"enterprise_id": "E04COREWEAVE"}` | ✅ 200 — credential stored |
+| `token_response_metadata: {"enterprise_id": "E99PERSONAL"}` | ❌ 403 — `'enterprise_id' = 'E99PERSONAL', expected 'E04COREWEAVE'` |
+| `token_response_metadata: {}` (field absent) | ❌ 403 — `required field 'enterprise_id' is absent` |
+
+## Common claim keys
+
+| Provider | Key | Example value |
+|----------|-----|---------------|
+| Slack | `enterprise_id` | `E04XXXXXXX` |
+| Jira / Confluence | `cloud_id` | `abc-123-def` |
+| GitHub Enterprise | `enterprise_id` | `your-org` |
+
+## Token Storage TTL
+
+Optionally set how long credentials are cached (in seconds):
+
+```json
+{
+  "token_validation": {"enterprise_id": "E04COREWEAVE"},
+  "token_storage_ttl_seconds": 3600
+}
+```