After migration, all posts and everything else now request credentials

What do you mean by that? Are you prompted to enter a password when you access the front end? And does this happen on every page?

If so, check the following:

• Look at a page in the back end to see if password protection is enabled there. If so, disable it and check if the front end works again.
• Check to see if you’ve installed a plugin that sets up password protection. Deactivate that plugin. If you can’t find one, deactivate all plugins as a test.