# Strange issue with Open OnDemand + mod\_auth\_mellon

**URL:** <https://discourse.openondemand.org/t/strange-issue-with-open-ondemand-mod-auth-mellon/4904>\
**Category:** Get Help\
**Created:** [June 24, 2026, 2:19pm UTC](https://discourse.openondemand.org/t/strange-issue-with-open-ondemand-mod-auth-mellon/4904 "2026-06-24T14:19:13Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Avinash-Komali](https://sea1.discourse-cdn.com/flex015/user_avatar/discourse.openondemand.org/avinash-komali/32/3439_2.png) [@Avinash-Komali](https://discourse.openondemand.org/u/Avinash-Komali)\
**Post date:** [June 24, 2026, 2:19pm UTC](https://discourse.openondemand.org/t/strange-issue-with-open-ondemand-mod-auth-mellon/4904/1 "2026-06-24T14:19:14Z")

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Hi All,

I’m seeing a strange issue with Open OnDemand + mod\_auth\_mellon on Ubuntu 24.04.

The exact same Entra ID / Mellon configuration works on another OOD deployment running in a Rocky Linux. However, on Ubuntu:

- `/mellon/metadata` works
- `/pun/sys/dashboard` redirects correctly to `/mellon/login`
- Entra authentication succeeds
- Browser POSTs to `/mellon/postResponse`
- `/mellon/postResponse` returns **HTTP 400 Bad Request**

Browser dev tools show:

- Request Method: `POST`
- `SAMLResponse` and `RelayState` are present

Ubuntu:

- Apache 2.4.58
- libapache2-mod-auth-mellon 0.19.0

Rocky (working):

- mod\_auth\_mellon 0.14.0

Has anyone seen `/mellon/postResponse` return 400 on Ubuntu while the same IdP configuration works on Rocky?

## Interesting Observation

If I access OOD via the “My Apps” application tile after authentication, the application works correctly.

However, direct access to:

```auto
https://<dns>.com/pun/sys/dashboard/

```

eventually results in the HTTP 400 response from `/mellon/postResponse`.

Any pointers would be appreciated.

Thanks!

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**Author:** ![jeff.ohrstrom](https://sea1.discourse-cdn.com/flex015/user_avatar/discourse.openondemand.org/jeff.ohrstrom/32/136_2.png) [@jeff.ohrstrom](https://discourse.openondemand.org/u/jeff.ohrstrom)\
**Post date:** [June 24, 2026, 3:52pm UTC](https://discourse.openondemand.org/t/strange-issue-with-open-ondemand-mod-auth-mellon/4904/2 "2026-06-24T15:52:05Z")

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I’d suggest increasing the logging level of `mod_auth_mellon`. That’s at least a start to figure out what it doesn’t like about the IdP’s response.