Currently, when external JSM customers with no Confluence product access), attempt to access a knowledge base space by logging into Confluence, they are prompted to request access to Confluence.

It will be a good option to have the mentioned customers access Confluence articles as viewers only. There is a Workaround provided in the article How JSM customers with an Atlassian account can view Confluence pages without having a license, however this cases this BUG when a custom domain is setup.