when to use openid.ax.required inopenid

Question

when to use openid.ax.required in making request for authentication.Because if this option is required by google but it is not required by yahoo.

Answer 1

It's never required to use AX. Google doesn't require it, neither does yahoo, or any other provider.

AX is an extension allowing you to fetch additional data, like user's name, or email.
openid.ax.required contains fields that you'd like to fetch and mark as required fields, that's it.

For more information, read the Attribute Exchange specification.