Feat: Allow custom HTTP client for JWKS fetching

[tanya732]

Changes

File	Purpose
JwksHttpClient.java	New @FunctionalInterface — the pluggable contract
JwksHttpResponse.java	Response value object carrying body + headers
DefaultJwksHttpClient.java	Extracted default impl preserving existing URLConnection behavior
JwkProviderBuilder.java	New .httpClient(JwksHttpClient) builder method
UrlJwkProvider.java	Delegates HTTP to JwksHttpClient; new 2-arg constructor
EXAMPLES.md	Usage examples for all four issues

Design decisions

• Zero breaking changes — existing code works identically; DefaultJwksHttpClient preserves prior behavior
• Zero new dependencies — users choose their own HTTP library
• httpClient() takes precedence over proxied(), timeouts(), headers() when set
• Response is String, not InputStream

Testing

Please describe how this can be tested by reviewers. Be specific about anything not tested and reasons why. If this library has unit and/or integration testing, tests should be added for new functionality and existing tests should complete without errors.

• This change adds test coverage
• This change has been tested on the latest version of Java or why not

Checklist

• I have read the Auth0 general contribution guidelines
• I have read the Auth0 Code of Conduct
• All existing and new tests complete without errors

[hvpareja]

Good job @tanya732 ! Thanks!!

[rmad17]

LGTM!