cannot open web, so can not approve new device

[giolong]

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Bug Report / Issue Description

Title: Cannot approve new device — web UI inaccessible

Description:

When setting up 9remote on a new machine, the tool requires opening a web interface to approve the new device. However, the web UI cannot be opened (e.g. running on a headless server with no browser), making it impossible to complete the device approval step. As a result, the session is permanently stuck and the tunnel cannot be established.

Environment:

• Tool: 9remote (latest)
• OS: Linux (headless / no GUI)
• cloudflared version: 2026.6.1

Steps to reproduce:

1. Install 9remote on a headless Linux server
2. Run 9remote start or equivalent command
3. Tool prompts for device approval via web UI
4. No browser is available to open the approval page
5. Device approval cannot be completed — tunnel never starts

Expected behavior:
A CLI-based approval flow, an approval token/flag, or a way to pre-authorize a device without requiring browser access.

Actual behavior:
The process hangs or exits waiting for web-based device approval with no alternative.

Possible workaround requested:

• A --approve or --headless flag
• Ability to approve via API or CLI
• Option to reuse an existing approved key without re-approval