Equally important to what Portier will do is what it will not do. Many of these decisions are taken in the interest of simplicity and maintainability: we want Portier to be as well-defined, understandable, and maintainable as possible. Thus, we explicitly reject features that would dramatically expand Portier's scope, increase its complexity, or require significant changes to its user experience.
Portier is a distinct tool, not an omnibus toolkit.
Specifically, Portier will not:
Provide profile metadata: Portier is narrowly focused on authenticating email addresses. Names, photos, and other metadata are out of scope.
Integrate with Facebook: People do not naturally think of their Facebook accounts as email addresses, while Portier is fundamentally driven by the notion of email address as identity. As such, direct integration with Facebook does not make sense for Portier. Websites may, of course, offer Facebook Connect as an authentication option alongside Portier.
Be a Single Sign-On service: Though Portier could be useful when build an SSO system, it is not itself an SSO system.
Remember multiple identities: Portier only verifies email addresses. It doesn't remember those addresses or make claims about associations between multiple addresses.
Promise native browser integration: Portier must work for everyone on the Web, regardless of browser. The complexity, bureaucracy, and time required for native integration is not currently worth its ill-defined benefits, especially with promising standards from the FIDO Alliance on the horizon. In contrast, Portier is relatively simple and designed to solve a specific problem today.
Protect users from their own email providers: A malicious email provider is able to impersonate users within its own domain, and may be able to observe where its users are logging in. However, this is true of all authentication systems with email-based account recovery workflows. Portier is not in a position to properly solve this problem.
Privacy-conscious users can control which parties they must trust by selecting a different email provider, or self-hosting their own domain.