[Fix] Add args for mTLS support (#3430)

Co-authored-by: declark1 <daniel.clark@ibm.com>

vllm/entrypoints/api_server.py

@@ -8,6 +8,7 @@ change `vllm/entrypoints/openai/api_server.py` instead.
 
 import argparse
 import json
+import ssl
 from typing import AsyncGenerator
 
 from fastapi import FastAPI, Request
@@ -86,10 +87,12 @@ if __name__ == "__main__":
                         type=str,
                         default=None,
                         help="The CA certificates file")
-    parser.add_argument("--ssl-cert-reqs",
-                        type=int,
-                        default=0,
-                        help="Whether client certificate is required")
+    parser.add_argument(
+        "--ssl-cert-reqs",
+        type=int,
+        default=int(ssl.CERT_NONE),
+        help="Whether client certificate is required (see stdlib ssl module's)"
+    )
     parser.add_argument(
         "--root-path",
         type=str,