feat(auth): add no-provider-auto-select flag to disable auto-redirect

[hrntknr]

Summary

Adds a --no-provider-auto-select flag that disables automatic redirect to the sole configured provider when no password is set. This gives operators the option to always land on the login chooser page even if only one provider is configured.

• AuthRouter: new noProviderAutoSelect field respected in handleLogin.
• mcp-proxy: thread flag into Run and auth.NewAuthRouter.
• Tests updated to cover both behaviors.
• Docs updated to document the new flag.

Type of Change

• feat: A new feature
• fix: A bug fix
• docs: Documentation only changes
• style: Changes that do not affect the meaning of the code (white-space, formatting, missing semi-colons, etc)
• refactor: A code change that neither fixes a bug nor adds a feature
• perf: A code change that improves performance
• test: Adding missing tests or correcting existing tests
• build: Changes that affect the build system or external dependencies
• ci: Changes to our CI configuration files and scripts
• chore: Other changes that don't modify src or test files
• revert: Reverts a previous commit

Related Issues

[codecov]

Codecov Report

❌ Patch coverage is 60.00000% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
main.go	0.00%	3 Missing ⚠️
pkg/mcp-proxy/main.go	0.00%	1 Missing ⚠️

📢 Thoughts on this report? Let us know!

[Copilot]

Pull Request Overview

This PR adds a new --no-provider-auto-select flag that gives operators control over authentication flow behavior by disabling automatic redirects to the sole configured OAuth/OIDC provider when no password is set.

• Added noProviderAutoSelect parameter throughout the authentication system
• Updated auto-redirect logic to respect the new flag setting
• Added comprehensive test coverage for different authentication scenarios

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
main.go	Added CLI flag definition and environment variable support for the new option
pkg/mcp-proxy/main.go	Threaded the new parameter through the Run function to auth router creation
pkg/auth/auth.go	Added noProviderAutoSelect field and implemented conditional auto-redirect logic
pkg/auth/auth_test.go	Added comprehensive tests covering auto-redirect behavior under different configurations
pkg/idp/idp_test.go	Updated test setup to pass the new parameter to maintain compatibility
docs/docs/configuration.md	Added documentation for the new configuration option

Comments suppressed due to low confidence (1)

docs/docs/configuration.md:1

• The table header separator line has inconsistent column count and alignment compared to the updated table structure. It should match the four-column format with proper alignment.

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