Fix CORS to allow DOCKER_HOST_ADDR for remote browser access

[shanemort1982]

Description

Fixes CORS errors when accessing OpenHands from a remote browser.

Problem

When accessing OpenHands from a remote machine, the browser shows CORS errors:

Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at http://192.168.1.206:42015/api/...
(Reason: CORS header 'Access-Control-Allow-Origin' missing)

The main OpenHands app runs on http://192.168.1.206:3000, but when it makes requests to agent-server containers (on different ports), the LocalhostCORSMiddleware blocks them because it only allows localhost and 127.0.0.1.

Root Cause

The LocalhostCORSMiddleware in middleware.py only checks for localhost/127.0.0.1 origins. When OpenHands is accessed via a server IP (e.g., 192.168.1.206), cross-origin requests from the main app to agent-server containers are blocked.

Solution

This PR adds support for the DOCKER_HOST_ADDR environment variable to the CORS middleware. When set, the middleware will also allow requests from that IP address.

Changes

• File: openhands-agent-server/openhands/agent_server/middleware.py
• Lines: Added import for os and check for DOCKER_HOST_ADDR (lines 1, 31-34)
• Impact: Minimal, safe change that extends CORS allowlist

Testing

Tested with:

• Server: 192.168.1.206
• Main app: http://192.168.1.206:3000
• Agent-server containers: Various ports (42015, 52051, etc.)
• Environment: DOCKER_HOST_ADDR=192.168.1.206

Before this fix: CORS errors block API requests from main app to agent-server
After this fix: Requests from 192.168.1.206:3000 to agent-server allowed

Related Issues

• Complements Fix WebSocket localhost bug by passing DOCKER_HOST_ADDR to runtime containers OpenHands#12113 (WebSocket localhost fix)
• Part of the solution for remote browser access

Backward Compatibility

• If DOCKER_HOST_ADDR is not set, behavior is unchanged
• No breaking changes
• Works with local (localhost) and remote deployments

Security Note

This change only allows cross-origin requests from the IP specified in DOCKER_HOST_ADDR. The middleware still:

• Requires explicit configuration (env variable must be set)
• Only allows the specific IP, not wildcard origins
• Maintains all other CORS security checks

[blacksmith-sh]

[Automatic Post]: I have assigned @xingyaoww as a reviewer based on git blame information. Thanks in advance for the help!

[blacksmith-sh]

[Automatic Post]: This PR seems to be currently waiting for review. @xingyaoww, could you please take a look when you have a chance?

[xingyaoww]

Thanks!

[all-hands-bot]

[Automatic Post]: It has been a while since there was any activity on this PR. @shanemort1982, are you still working on it? If so, please go ahead, if not then please request review, close it, or request that someone else follow up.