MVC 4 OAuth: How to get e-mail address

Question

I am developing an MVC 4 app and use the OAuth providers provided by MS, but I would like to get an e-mail address for every user. For Google (default) and Facebook (using FacebookClient) I already get the users address, but what to do about the following:

• Twitter (I have read it is not possible - still true?)
• Microsoft - solved (see comments)
• Yahoo - works (see comment)
• LinkedIn - solved via own provider like for MS

And what about, when it is not possible via OAuth like with Twitter?
I've read in different threads it is not good/secure to just ask the user for it. Is it "secure enough" if I also require a verification via e-mail to actually use the address (but not the account in general) as I (will) do when changing the address?

Answer 1

The purpose of OAuth is not to provide email addresses, its to provide authentication in a standardized way. Just because a lot of the implementations also happen to give you the option of an email address doesn't mean that all of them must comply. Twitter is a case in point.

Why would asking a user for their email address not be "secure"? I would question that, I mean if you can't trust a users input regarding their email address, what can you trust them with? If you're using some sort of confirmation mail system it would surely be fine?