Open Keycloak

Select or Create a new Realm in KeyCloak

Copy the link pointing to the SAML 2.0 Identity Provider Metadata 

This is a url : <keycloak-url>/auth/realms/<realm-name>/protocol/saml/descriptor

Open the Atlassian Application

Select the URL option as Identity Provider and paste the in the link 

and press on Save

Copy the SP XML and create a new File e.g. sp.xml and paste the content in this file

If you don't see the SP Certificate, log out and log in again

Open Keycloak

Select Clients and Create a new Client

Import the sp.xml file and click on Save

Put Client Signature Required and put it on OFF and save again

Open Atlassian Application

Log out and Click on the Button Login using SAML IDP Server

this should redirect to keycloak

Further Configuration :