Streamable HTTP / DCR not supported? Error: Failed to connect to MCP server "semilattice": token_endpoint_auth_method: Input should be 'none' or 'client_secret_post'

[jtewright]

Before opening, please confirm:

• I have searched for duplicate or closed issues

Operating System

MacOS 26.1 (25B78)

Kiro Version

Version: 0.6.0

Bug Description

Testing Kiro with an MCP (config below). I get the error: "Failed to connect to MCP server "semilattice": token_endpoint_auth_method: Input should be 'none' or 'client_secret_post'".

"semilattice": {
      "url": "https://mcp.semilattice.ai",
      "type": "http", 
      "disabled": false
    }

Note, your docs don't say to add "type": "http", that was me trying to get this to work. Same error if "type" is omitted.

This MCP uses fastmcp under the hood and implements their OAuthProxy for DCR Dynamic Client Registration. It triggers an OAuth flow.

Note, this works in vanilla VS Code.

Kiro logs:

2025-11-18 14:21:19.669 [info] [semilattice] Adding new MCP server from updated configuration
2025-11-18 14:21:19.669 [info] [semilattice] Registering MCP server and starting connection
2025-11-18 14:21:19.851 [info] [semilattice] MCP connection closed successfully
2025-11-18 14:21:19.852 [error] [semilattice] Error connecting to MCP server: token_endpoint_auth_method: Input should be 'none' or 'client_secret_post'

Steps to Reproduce

1. Add streamable http oauth dcr mcp
2. Attempt to connect

Expected Behavior

Browser opens, oauth flow, back to Kiro and you're connected

Conversation ID

No response

Additional Context

No response

[TheAlanNix]

Getting the same issue with the Wiz MCP server. The OAuth configuration for the server provides the following supported auth methods:

"token_endpoint_auth_methods_supported": [
    "none",
    "client_secret_post"
 ]

But then it appears Kiro ignores that, and hits the registration endpoint with a request payload that contains the following:

"token_endpoint_auth_method": "client_secret_basic"

The Wiz MCP server then replies back with Invalid token_endpoint_auth_method

[TheAlanNix]

Upgraded to 0.8.140 this morning and it looks like this was resolved.

[v4de]

I have this issue with ado mcp. Kiro does not support DCR or pre-registered OAuth client. Vscode has implemented it with github copilot (RFC 7591)

    "ado-http": {
      "url": "https://mcp.dev.azure.com/{organization}",
      "type": "http",
      "disabled": false
    },

[2026-03-26T16:31:37.280Z] [error] [ado-http] Error connecting to MCP server: Incompatible auth server: does not support dynamic client registration

[AnilMaktala]

@TheAlanNix confirmed this was resolved back in 0.8.140. Closing as completed — the client_secret_post auth method support has been stable since then and further improved in CLI 2.12.0.