fix: ignore undefined external auth provider

[sweatybridge]

What kind of change does this PR introduce?

Bug fix

What is the new behavior?

Allows external auth config to be undefined to use platform defaults.

Additional context

Add any other context or screenshots.

[coveralls]

Pull Request Test Coverage Report for Build 12215846069

Details

• 141 of 243 (58.02%) changed or added relevant lines in 2 files are covered.
• 7 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.07%) to 59.864%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/config/auth.go	140	242	57.85%

Files with Coverage Reduction	New Missed Lines	%
internal/storage/rm/rm.go	2	89.53%
internal/gen/keys/keys.go	5	12.9%

Totals
Change from base Build 12215610642:	-0.07%
Covered Lines:	7638
Relevant Lines:	12759

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💛 - Coveralls