The problem is, there is no standard for truly owned identities besides usernames and passwords, and those are frowned upon as &quot;different accounts&quot;. And many services seem to not want any interoperability at authentication layer and to accept third party (esp. competitors&#x27;) assertions as credentials.<p>This applies to Slack too - to best of my knowledge, one can&#x27;t log in there, using, say, GitHub identity assertion as a credential.<p>But I&#x27;m not sure how Slack has anything to do with this. You&#x27;re right. They&#x27;re just a yet another platform with its own non-interoperable account system. Don&#x27;t see how it&#x27;s better than anything other, except when <i>everyone</i> is already there, which I find hard to believe. (But any other platform that knows how to consume external credentials is wins in this regard.)