Re: Alfresco share - Getting Basic authentication prompt after external SSO login for proxy/alfresco/api/...
Step 1: Provide useful / actionable information when asking on a public forum. I.e.:
What kind of SSO did you configure / enable? You say "external SSO", but the configuration in share-config-custom.xml also uses an "external-auth" section when Kerberos / NTLM are being used, so it would be ideal if you could clarify which subsystem you have enabled...
Did you properly configure the "Remote" config section, especially the endpoints therein, as described in the official documentation? WIthout using the correct endpoint (i.e. /alfresco/wcs/) and making sure to use sessions as well as "external-auth" set to true, you may encounter potential issues.
Are you by any chance using a proxy / web server in front of Alfresco which may be dropping the session, or - in case of a clustered Alfresco - be redirecting the request to a different backend (session stickyness is a must in this use case)?