(docs) Simplify /vertex_ai/ pass through docs (#6910)

* simplify vertex pass through docs

* allow using known path for setting up pass throughs

* add unit testing for vtx pass through auth

litellm/proxy/vertex_ai_endpoints/vertex_endpoints.py

@@ -28,25 +28,54 @@ from litellm.proxy.auth.user_api_key_auth import user_api_key_auth
 from litellm.proxy.pass_through_endpoints.pass_through_endpoints import (
     create_pass_through_route,
 )
+from litellm.secret_managers.main import get_secret_str
+from litellm.types.passthrough_endpoints.vertex_ai import *
 
 router = APIRouter()
-default_vertex_config = None
+
+default_vertex_config: VertexPassThroughCredentials = VertexPassThroughCredentials()
 
 
-def set_default_vertex_config(config):
+def _get_vertex_env_vars() -> VertexPassThroughCredentials:
+    """
+    Helper to get vertex pass through config from environment variables
+
+    The following environment variables are used:
+    - DEFAULT_VERTEXAI_PROJECT (project id)
+    - DEFAULT_VERTEXAI_LOCATION (location)
+    - DEFAULT_GOOGLE_APPLICATION_CREDENTIALS (path to credentials file)
+    """
+    return VertexPassThroughCredentials(
+        vertex_project=get_secret_str("DEFAULT_VERTEXAI_PROJECT"),
+        vertex_location=get_secret_str("DEFAULT_VERTEXAI_LOCATION"),
+        vertex_credentials=get_secret_str("DEFAULT_GOOGLE_APPLICATION_CREDENTIALS"),
+    )
+
+
+def set_default_vertex_config(config: Optional[dict] = None):
+    """Sets vertex configuration from provided config and/or environment variables
+
+    Args:
+        config (Optional[dict]): Configuration dictionary
+        Example: {
+            "vertex_project": "my-project-123",
+            "vertex_location": "us-central1",
+            "vertex_credentials": "os.environ/GOOGLE_CREDS"
+        }
+    """
     global default_vertex_config
-    if config is None:
-        return
 
-    if not isinstance(config, dict):
-        raise ValueError("invalid config, vertex default config must be a dictionary")
+    # Initialize config dictionary if None
+    if config is None:
+        default_vertex_config = _get_vertex_env_vars()
+        return
 
     if isinstance(config, dict):
         for key, value in config.items():
             if isinstance(value, str) and value.startswith("os.environ/"):
                 config[key] = litellm.get_secret(value)
 
-    default_vertex_config = config
+    default_vertex_config = VertexPassThroughCredentials(**config)
 
 
 def exception_handler(e: Exception):
@@ -140,7 +169,7 @@ async def vertex_proxy_route(
     vertex_project = None
     vertex_location = None
     # Use headers from the incoming request if default_vertex_config is not set
-    if default_vertex_config is None:
+    if default_vertex_config.vertex_project is None:
         headers = dict(request.headers) or {}
         verbose_proxy_logger.debug(
             "default_vertex_config  not set, incoming request headers %s", headers
@@ -153,9 +182,9 @@ async def vertex_proxy_route(
         headers.pop("content-length", None)
         headers.pop("host", None)
     else:
-        vertex_project = default_vertex_config.get("vertex_project")
-        vertex_location = default_vertex_config.get("vertex_location")
-        vertex_credentials = default_vertex_config.get("vertex_credentials")
+        vertex_project = default_vertex_config.vertex_project
+        vertex_location = default_vertex_config.vertex_location
+        vertex_credentials = default_vertex_config.vertex_credentials
 
         base_target_url = f"https://{vertex_location}-aiplatform.googleapis.com/"