One of the biggest bug-bears of PowerApps is that it doesn't support guest, or unauthenticated access. This is a problem because it makes it difficult to share apps with external users who are not part of your organization. As an example, imagine if we were to create a survey app and we wanted to allow anonymous users to complete the survey, this wouldn't be possible under the current security model.

Until now, one workaround is to create a shared Office 365 user and to share those credentials with the users that require access to your app. 

I've been loathe to recommend this technique because it isn't clear exactly what is acceptable under the terms of the licensing agreement.

As a brief summary, here's a screenshot of some of the conversation. Guest access will be a fantastic enhancement and I look forward to this.