Add auto_error to security utils

[tiangolo]

✨ Add auto_error to security utils to allow them to be optional, also allowing the declaration of multiple security schemes.

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When setting auto_error=False, instead of raising/returning an HTTP 403 "Not authenticated" error to the client, it returns None to the parameter in a path operation function or dependency.

This makes it possible to have optional authentication.

It also allows to declare multiple optional security schemes in a dependency. And then, inside of the dependency, enforce that at least one is provided/validated. This can be used when allowing authentication with username/password using OAuth2PasswordBearer but also with other OAuth2 providers (Google, Facebook, etc).

To use it, in the security utils, instead of writing:

oauth2_scheme = OAuth2PasswordBearer(tokenUrl="/token")

write:

oauth2_scheme = OAuth2PasswordBearer(tokenUrl="/token", auto_error=False)

It can also be used to customize the error returned, overwriting the default "Not authenticated" with something different, by taking the result of the dependency and if it's None, raising an HTTPException with a custom detail message.

[codecov]

Codecov Report

Merging #134 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #134    +/-   ##
======================================
  Coverage     100%   100%            
======================================
  Files         127    137    +10     
  Lines        3037   3404   +367     
======================================
+ Hits         3037   3404   +367

Impacted Files	Coverage Δ
tests/test_security_http_digest_optional.py	100% <100%> (ø)
tests/test_security_http_base_optional.py	100% <100%> (ø)
tests/test_security_oauth2_optional.py	100% <100%> (ø)
fastapi/security/api_key.py	100% <100%> (ø)	⬆️
tests/test_security_openid_connect_optional.py	100% <100%> (ø)
tests/test_security_http_bearer_optional.py	100% <100%> (ø)
fastapi/security/http.py	100% <100%> (ø)	⬆️
...s/test_security_oauth2_password_bearer_optional.py	100% <100%> (ø)
tests/test_security_api_key_query_optional.py	100% <100%> (ø)
tests/test_security_api_key_cookie_optional.py	100% <100%> (ø)
... and 14 more

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