Only allow PublicAuthOptions to be accessed in Razor pages

[Nateowami]

GetAuthOptions had a return type of PublicAuthOptions, but was returning all auth options (since AuthOptions extends PublicAuthOptions, the types are compatible). In practice this doesn't leak anything to the Razor pages unless the object is serialized, but since the entire purpose of PublicAuthOptions is to limit what is provided to the Razor pages, it seems more complete to not even allow the secrets to be available in the scope of the templates.

@pmachapman What do you think? Too pedantic, or reasonable change?

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This change is 

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.82%. Comparing base (dd2b2cb) to head (45f5899).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3623   +/-   ##
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  Coverage   82.82%   82.82%           
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  Files         610      610           
  Lines       37414    37420    +6     
  Branches     6152     6128   -24     
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+ Hits        30987    30993    +6     
  Misses       5494     5494           
  Partials      933      933           

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[pmachapman]

It would only leak if you recast the object as as AuthOptions, then serialized. Razor pages are generated on the server-side, so it would have to be a very conscious effort of the programmer. I don't see the harm in your approach, though, so

@pmachapman reviewed 1 file and all commit messages, and made 1 comment.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @Nateowami).