Revert "Solid build, authentication (typo) problem fixed. Into Lesson 21"

This reverts commit 22a67425b3275300395960bb6ae441e8ecfe0952.
Revert "Into Lesson 21, but have just discovered authentication errors that go back to Lesson 19"

This reverts commit 2ead5136290ccefdbf5094b3b90525ca6fbb46c3.
Into Lesson 21, with image errors.