[FEATURE] Add `claude mcp auth` command for CLI-based authentication

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

There is currently no way to trigger MCP server authentication from the command line. The only way to authenticate an MCP server that requires OAuth is to start a session and initiate the flow via /mcp.

Proposed Solution

Add an auth (or login) subcommand to claude mcp: ``bash # Trigger the OAuth flow for a specific MCP server claude mcp auth <server-name> ``

Alternative Solutions

_No response_

Priority

Medium - Would be very helpful

Feature Category

CLI commands and flags

Use Case Example

_No response_

Additional Context

This is a resubmission of #23512 and #6057 that were closed inappropriately due to #16497, which has now been fixed in #26360.