I have an old application that uses AuthSub to authenticate with Google and upload videos to a YouTube account. When I linked my YouTube account to a Google+ Page, I could no longer upload videos to that channel because I can only choose Google Accounts and not Google+ Pages on the AuthSub account chooser page. How can I make my app authenticate as the Google+ Page?
Related YouTube Google+ Integration community post: https://plus.google.com/109134699638863873361/posts/AcqYTcrc4Go
The recommended course of action is to migrate to OAuth 2. OAuth 2 supports a channel-picker that will let you authorize applications to make requests for any of the channels you have access to, either associated with your own Google Account or via Google+ Pages.
I understand that that migrating to OAuth 2 might take some time for some developers, or maybe you're not the developer but rather a user of an application that is still using a legacy authorization flow like AuthSub. In those cases, what you need to do is assign a password to the Google Account associated with your Google+ Page, as described in this help center article. When using ClientLogin, OAuth 1, or AuthSub, you'd supply the Google Account email address and password that you set up for the Google+ Page.
We're going to have something on the YouTube API Blog in the near future that talks about best practices for working with +Page channels in more detail.
