Add Bearer Authentication to the MCP server plugin

[zeroSteiner]

Description

This adds bearer authentication to the MCP server started by the plugin, bringing it inline with the same behavior added in #21527. The value meanings are the same, by default a random token is generated, if the user explicitly sets a blank value, authentication is disabled otherwise the token is used as-is.

Related Issue:

Breaking Changes

None

Reviewer Notes

Verification Steps

Use the same steps from #21527

1. • Load the plugin
2. • Start the server by default, see a randomly generated API token displayed
3. • Stop the server and restart it, adding AuthToken= to the end, see that now authentication is disabled
4. • Stop the server and restart it, adding AuthToken=whatever to the end, see that now authentication is enabled, and the token is not echoed back to the user. They gave it to us, they know it, we don't need to be logging it anywhere.

Test Evidence

msf exploit(windows/smb/psexec) > load mcp
[*] MCP plugin loaded. Use mcp start to start the server.
[*] Successfully loaded plugin: mcp
msf exploit(windows/smb/psexec) > mcp start
[*] Auto-started msgrpc - User: msf, Pass: 2MXwknnMf7zy
[*] MCP server listening on http://localhost:3000/
[*] Authentication: Bearer token (auto-generated)
[*]   Configure your MCP client with: Authorization: Bearer 43b93f53b68816f30dff19058fb4f676234e1943dc67ffa232b53b7a3e96733d
[*] Starting MCP server on HTTP transport...
msf exploit(windows/smb/psexec) > mcp stop
[*] MCP server stopped
msf exploit(windows/smb/psexec) > mcp start AuthToken=
key: "AuthToken" value: ""
[*] MCP server listening on http://localhost:3000/
[*] Authentication: disabled
[*] Starting MCP server on HTTP transport...
msf exploit(windows/smb/psexec) > mcp restart AuthToken=imhungryisitlunchtimeyet
[*] MCP server listening on http://localhost:3000/
[*] Authentication: enabled
[*] Starting MCP server on HTTP transport...
msf exploit(windows/smb/psexec) >

Environment

Field	Details
Operating System	Fedora
Target Software/Hardware	N/A
Docker Image / Vagrant Setup

AI Usage Disclosure

Did everything by hand.

Pre-Submission Checklist

• Included a corresponding documentation markdown file in documentation/modules (new modules only)
• No sensitive information (IP addresses, credentials, API keys, hashes) in code or documentation
• Tested on the target environment specified in the Environment section above
• Included RSpec tests for library changes (encouraged for lib/ changes)
• Read the CONTRIBUTING.md and module acceptance guidelines

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[zeroSteiner]

While this code is duplicated, I took care so that what is printed is consistent between the plugin and the msfmcpd stand-alone utility, so it's not visually obvious that they're different.

[sjanusz-r7]

Two things came up during testing:

• Loading mcp plugin, calling mcp start results in Ctrl + C interrupt not working:

msf auxiliary(scanner/discovery/udp_sweep) > Interrupt: use the 'exit' command to quit
msf auxiliary(scanner/discovery/udp_sweep) > mcp start
[*] Auto-started msgrpc - User: msf, Pass: x
[*] MCP server listening on http://localhost:3000/
[*] Authentication: Bearer token (auto-generated)
[*]   Configure your MCP client with: Authorization: Bearer x
[*] Starting MCP server on HTTP transport...
msf auxiliary(scanner/discovery/udp_sweep) > // Ctrl + C does nothing here, even after calling `mcp stop`

• I can start up the mcp daemon and the mcp plugin together, both report as listening:

## Tab 1
bundle exec ./msfmcpd --mcp-transport http
...
MCP server listening on http://localhost:3000/

## Tab 2
msf auxiliary(scanner/discovery/udp_sweep) > mcp start
[*] MCP server listening on http://localhost:3000/
[*] Authentication: Bearer token (auto-generated)
[*]   Configure your MCP client with: Authorization: Bearer x
[*] Starting MCP server on HTTP transport...

I expected the second tab to fail, as the address is already in use.

Otherwise, the bearer auth tests:

Default auto-generated token

// No token
curl http://localhost:3000/
{"error":"Unauthorized"}

// Correct token
curl -H "Authorization: Bearer foo" http://localhost:3000/
{"error":"Missing session ID"}

// Incorrect token
curl -H "Authorization: Bearer wrong_foo" http://localhost:3000/
{"error":"Unauthorized"}

Custom Token

Starting:

mcp start AuthToken='foo'
[*] MCP server listening on http://localhost:3000/
[*] Authentication: enabled
[*] Starting MCP server on HTTP transport...

Then:

// No token
curl http://localhost:3000/
{"error":"Unauthorized"}

// Correct token
curl -H "Authorization: Bearer foo" http://localhost:3000/
{"error":"Missing session ID"}

// Wrong token
curl -H "Authorization: Bearer wrong_foo" http://localhost:3000/
{"error":"Unauthorized"}

No auth token

Starting:

mcp start AuthToken=''
[*] MCP server listening on http://localhost:3000/
[*] Authentication: disabled
[*] Starting MCP server on HTTP transport...

Then:

// No token
curl http://localhost:3000/                               
{"error":"Missing session ID"}

// Any token provided
curl -H "Authorization: Bearer foo" http://localhost:3000/
{"error":"Missing session ID"}