### What version of Codex is running? codex-cli 0.46.0 ### Which model were you using? gpt-5-codex medium ### What platform is your computer? Darwin 24.6.0 arm64 arm ### What steps can reproduce the bug? Configuring [todoist mcp](https://github.com/Doist/todoist-ai) using the experimental RMCP client ```toml experimental_use_rmcp_client = true [mcp_servers.todoist] url = "https://ai.todoist.net/mcp" ``` and then running ```bash codex mcp login todoist ``` ### What is the expected be

Failing to login with OAuth in MCP HTTP server

Resolved 💬 3 comments Opened Oct 10, 2025 by ilmeskio Closed Oct 15, 2025

💡 Likely answer: A maintainer (gpeal, contributor) responded on this thread — see the highlighted reply below.

What version of Codex is running?

codex-cli 0.46.0

Which model were you using?

gpt-5-codex medium

What platform is your computer?

Darwin 24.6.0 arm64 arm

What steps can reproduce the bug?

Configuring todoist mcp using the experimental RMCP client

experimental_use_rmcp_client = true

[mcp_servers.todoist]
url = "https://ai.todoist.net/mcp"

and then running

codex mcp login todoist

What is the expected behavior?

Browser opens (I am using Arc browser)
Login and authorize
Close browser and get to terminal
Login in mcp confirmed

What do you see instead?

Browser opens (I am using Arc browser)
Login and authorize
Close browser and get to terminal

In terminal I see

Error: failed to handle OAuth callback

Caused by:
    OAuth token exchange failed: Server returned error response: Required argument is missing

Additional information

_No response_

View original on GitHub ↗

3 Comments

scottlovegrove · 10 months ago

It looks like the issue here is that Codex is ignoring what the supported token_endpoint_auth_methods_supported is on our [Todoist] well-known file.

We currently only support oauth_token_post and it seems that Codex is _only_ trying it based on oauth_token_basic, as seen in this screenshot:
<img width="1075" height="972" alt="Image" src="https://github.com/user-attachments/assets/324258aa-135e-4cff-9c53-b9c1340973f9" />

We are discussing internally around adding oauth_token_basic support on our side, which would fix the Todoist-specific error, but this may still affect other authentication servers that only support oauth_token_post.

gpeal contributor · 10 months ago

Thanks for the report and the analysis. We'll look into this on our side as well

gpeal contributor · 10 months ago

It looks like todoist added support for client_secret_basic and I can confirm that the MCP server works. I'm actually going to close this out for now because all of the other MCPs I try also support this so I no longer have a good repro server to test against.

If somebody from todoist wants to stand up a test one somewhere or if somebody find another public MCP server that this is an issue for, feel free to reopen.