[BUG] microsoft365 MCP: OAuth flow fails with two distinct errors

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

The Microsoft 365 MCP server (https://microsoft365.mcp.claude.com/mcp) authentication
flow is broken. Calling mcp__microsoft365__authenticate produces a URL with two separate
issues that prevent login from completing.

What Should Happen?

The OAuth flow completes successfully and the Microsoft 365 MCP tools become available in Claude Code.

Error Messages/Logs

Steps to Reproduce

Add the microsoft365 MCP server to Claude Code.

1. Invoke the authentication tool (mcp__microsoft365__authenticate).
2. Open the generated authorization URL in a browser.

## Issue 1 — Duplicate prompt parameter

The generated URL contains prompt twice:

?prompt=select_account&...&prompt=consent

Microsoft's identity platform rejects this with:

AADSTS9000411: The request is not properly formatted.
The parameter 'prompt' is duplicated.

Workaround attempted: Manually removed the first prompt=select_account from the URL
and retried.

## Issue 2 — Unregistered redirect_uri

After fixing Issue 1 manually, login proceeds but fails at redirect with:

AADSTS900971: No reply address provided.

The generated redirect_uri uses a dynamic localhost port
(e.g. http://localhost:44974/callback). This URI does not appear to be registered
in the Azure AD app registration for client_id 08ad6f98-a4f8-4635-bb8d-f1a3044760f0.

For public client apps, Azure AD supports dynamic localhost ports natively
(http://localhost without a fixed port), but only if the app is registered
as a public client with that base URI.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

latest

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

_No response_