AdkApp: user_id always defaults to 'default-user-id' when called from Google Agentspace

[caohy1988]

Environment

Component	Value
Package	google-cloud-aiplatform
File	vertexai/agent_engines/templates/adk.py
Python	3.12
Deployment	Vertex AI Agent Engine via Agentspace

Description

When ADK agents are deployed to Google Agentspace and users interact through the Agentspace UI, user_id is always "default-user-id" for all sessions and events. The real user identity (IAM principal/email) is never propagated, making per-user analytics impossible.

Root cause

In vertexai/agent_engines/templates/adk.py, line 97:

_DEFAULT_USER_ID = "default-user-id"

The _StreamRunRequest constructor (lines 198-200) falls back to this default:

self.user_id: Optional[str] = kwargs.get("user_id") or kwargs.get(
    "userId", _DEFAULT_USER_ID
)

When Agentspace calls streaming_agent_run_with_events(request_json) (line 1166), the incoming JSON does not include a user_id or userId field. The authenticated user's identity — which Agentspace does know (confirmed by useriamprincipal in discoveryengine.googleapis.com audit logs) — is not passed through to the Agent Engine request payload.

This "default-user-id" then propagates through the entire ADK stack:

_StreamRunRequest.user_id ("default-user-id")
  → Runner.run_async(user_id=...)
    → Session.user_id
      → InvocationContext.user_id
        → BigQueryAgentAnalyticsPlugin logs it to BQ

Expected behavior

When a user accesses an agent through Agentspace, the user_id field in the request should contain the authenticated user's identity (IAM principal or email). The identity is already available in the Agentspace request context — it just needs to be included in the streaming_agent_run_with_events request JSON.

Possible fixes

1. Agentspace side: Include the authenticated user's identity in the user_id field of the request JSON sent to Agent Engine
2. Vertex AI SDK side: In streaming_agent_run_with_events() or _StreamRunRequest, extract user identity from HTTP request headers or IAM metadata as a fallback, rather than using a hardcoded "default-user-id"

Impact

• All ADK agents deployed to Agentspace are affected
• BigQueryAgentAnalyticsPlugin logs "default-user-id" for all events, breaking per-user analytics (token usage, session counts, agent adoption)
• Any downstream system relying on session.user_id gets the placeholder value

Related

• Originally reported as BigQueryAgentAnalyticsPlugin user_id always logs default-user-id when agents are accessed via Google Agentspace google/adk-python#5189 — closed with a pointer to this issue since the root cause is in the Vertex AI SDK, not in ADK