Cookie length should be less than or equal to 4096

Your Kibana does not listen in https, does it? If not, why do you have protocol: https?
Also, check the issuer. Where did you get that from?

Also please let’s try with the latest ROR build and see if the stacktrace is still there and similar:

This is protocol for SAML provides, isn’t it?
External kibana endpoint is HTTPS, server listen in HTTP.
I can’t download latest release, can you update a link?

I’m referring to readonlyrest_kbn.auth.saml_kc.protocol which specifies the Kibana web server protocol.

Please test this other trial build: