In addition to questions rised by Michael above, could you also expand a bit on your current setup?
>I have followed both Gitlab and Gluu docs to setup SAML SSO up to the point where I can initiate a request to the Gluu server from Gitlab
Could you provide links to all documentation you were trying to follow? One thing I would like you to dismiss is that whether or not Passport-SAML takes any part in your flow, as I see its script enabled on one of your screenshots. Despite this, it seems like you try to configure regular SAML Trust Relationship (i.e. Outbound SAML flow)
The HAR file you provided contains only the final few requests (error from Gitlab), with no context. Please capture the failing flow again, using steps listed [here](https://www.inflectra.com/support/knowledgebase/kb254.aspx) - please use Firefox for that task, Chrome's HARs are flawed. Also don't forget to set "Persist log" and "Disable cache" checkboxes in the console to save everything, not just the recently loaded page.
Also, make sure you set "Encrypt assertions" to "never" in Relying Party Configuration for this TR before proceeding with the capture and restart "idp" service after applying the changes.
Finally, I've noted that your HAR capture doesn't seem to be taken at the same moment as your log files (03.07 vs 03.06). Please make sure you gather your logs around the same time you export the HAR file, we need to see corellations between those.
Overall, it seems you are currently sending nameid of type "transient" to Gitlab, and no attributes whatsoever - despite I see "Email" attribute in your "Released" list. Have you tried to restart "idp" service since the moment you added this attribute to the list?