Select the closest auth according to auth type

[lykling]

• If token auth is not main_auth with customized header, then selected_auth will always be main_auth
• If digest auth is not main_auth, it return main_auth too, because there may no Authorization header in the first request of digest auth

[codecov-io]

Codecov Report

Merging #125 (ea562ec) into master (ccf98aa) will decrease coverage by 3.33%.
The diff coverage is 70.00%.

@@             Coverage Diff             @@
##            master     #125      +/-   ##
===========================================
- Coverage   100.00%   96.66%   -3.34%     
===========================================
  Files            1        1              
  Lines          254      270      +16     
  Branches        34       40       +6     
===========================================
+ Hits           254      261       +7     
- Misses           0        6       +6     
- Partials         0        3       +3     

Impacted Files	Coverage Δ
flask_httpauth.py	96.66% <70.00%> (-3.34%)	⬇️

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[miguelgrinberg]

While I like that you have made it possible to include auth objects that use custom headers, overall I find that this is a fairly big change and that the same could be achieved by just making a small change while keeping the current logic of the multi auth object. In particular I do not like that you have removed the concept of a main auth object and replaced it with auth[0], which is obscure.

I will take it as a feature request for the custom header support and re-implement this, if you don't mind. If there is any other aspect of this change that you think important to preserve let me know.