问题
when to use http://schema.openid.net/contact/email and when to use http://axschema.org/contact/email in openid request.
回答1:
Unfortunately there is no standard schema for Attribute Exchange (AX). But the axschema.org seems to be the closest thing to it. To know which one to use, the best way I know of is to look for a "hint" about which schema(s) are supported in the OP's XRDS document. DotNetOpenAuth does this, for example, and has a good success rate. When the XRDS doesn't contain any of the AX schema URIs, you can send all three (yes, there are three) AX attribute URI formats to best ensure a useful response.
回答2:
Nowadays, it seems the preferred AX schema url is always schema.openid.net. The axschema.org domain has been down for almost a year (not that it's needed).
Refs: Chris Messina on OpenID list and StackOverflow: Google only responds to schema.openid.net.
来源：https://stackoverflow.com/questions/3284312/difference-between-http-schema-openid-net-contact-email-and-http-axschema-or