[BUG] SAML endpoint still using _opendistro instead of _plugins

[spicycanary91]

Describe the bug

Opensearch-Desktop does not operate as expected using saml authentication. It is still referring to the _opendistro endpoint instead of the _plugins endpoint.
The documentation link explains to use the /_plugins/_security/saml/acs endpoint to whitelist / configure sp metadata in the idp. This does not work at the moment. Dashboards produces a saml request using opendistro endpoints instead: https://dashboards.domain.com/_plugins/_security/saml/acs
This causes a browser error:
{ statusCode: 400, error: "Bad Request", message: "Request must contain a osd-xsrf header." }
The idp logs an error since the opendistro endpoint does not exist in it's configuration:
auth request:AssertionConsumerServiceURL="https://dashboards.domain.com/_opendistro/_security/saml/acs"

However, configuring everything the opendistro way somewhat works. It causes 401 errors when trying to refresh the cookie at times but initial authentication works.

To Reproduce
Migrate from latest opendistro to opensearch 1.0.1 (In this case using the the official docker containers).
Configure saml integration as per new plugin documentation.
Check saml assertion in browser using the "SAML message decoder" extension.
Notice that it referrers to the _opendistro endpoint and not the _plugins endpoint.

Expected behavior
SAML to use the /_plugins/_security/saml/acs endpoint instead of the /_opendistro/_security/saml/acs one as described in the documentation.

OpenSearch Version
docker 1.0.1
Dashboards Version
docker 1.0.1
Plugins
as per docker 1.0.1
Please list all plugins currently enabled.
default docker setup

Host/Environment (please complete the following information):

• OS: docker image
• Browser and version: Chrome 94

Additional context

We have a discussion in the forum about this and saml related issues
https://discuss.opendistrocommunity.dev/t/saml-cookie-refresh-sso-redirect-issue-worked-before-upgrade

[kavilla]

Hello @spicycanary91,

Although that header comes from this project this is related to security plugin.

@opensearch-project/admin could you re-route this to https://github.com/opensearch-project/security-dashboards-plugin

[spicycanary91]

Thank you!

Not a problem. Moved to
opensearch-project/security-dashboards-plugin#836