Hi,

     I don't think substitute server authorization is a problem. In
most cases, the purpose of using a substitute server in the installation
process is mainly for speeding up package downloads. The content of the
substitute server mirror remains the same as the official one. As I
know, in that case, the authorization is not necessary. So that adding a
substitute server option in the graphical installer is reasonable. It
would improve the convenience radically, especially for people in some
countries or regions where a fast internet connection to the official
server is not available.

ZeroBeyond