V2: Login Feature (#4701)

This PR migrates the login features from V1 into V2.

  ---
- Login via username/password
- SSO login (Google & GitHub)
-- Fixed issue where users authenticating via SSO (OAuth2/SAML2) were
identified by configurable username attributes (email,
preferred_username, etc.), causing:
  - Duplicate accounts when username attributes changed
  - Authentication failures when claim/NameID configuration changed
  - Data redundancy from same user having multiple accounts
- Added `sso_provider_id` column to store provider's unique identifier
(OIDC sub claim / SAML2 NameID)
- Added `sso_provider` column to store provider name (e.g., "google",
"github", "saml2")
  - User.java:65-69

  Backend Changes:
- Updated UserRepository with findBySsoProviderAndSsoProviderId() method
(UserRepository.java:25)
- Modified UserService.processSSOPostLogin() to implement lookup
priority:
    a. Find by (`ssoProvider`, `ssoProviderId`) first
    b. Fallback to username for backward compatibility
c. Automatically migrate existing users by adding provider IDs
(UserService.java:64-107)
- Updated saveUserCore() to accept and store SSO provider details
(UserService.java:506-566)

  OAuth2 Integration:
- CustomOAuth2UserService: Extracts OIDC sub claim and registration ID
(CustomOAuth2UserService.java:49-59)
- CustomOAuth2AuthenticationSuccessHandler: Passes provider info to
processSSOPostLogin()
(CustomOAuth2AuthenticationSuccessHandler.java:95-108)

  SAML2 Integration:
- CustomSaml2AuthenticationSuccessHandler: Extracts NameID from SAML2
assertion (CustomSaml2AuthenticationSuccessHandler.java:120-133)

  ---
- Configurable Rate Limiting

  Changes:
- Added RateLimit configuration class to ApplicationProperties.Security
(ApplicationProperties.java:314-317)
- Made reset schedule configurable: security.rate-limit.reset-schedule
(default: "0 0 0 * * MON")
- Made max requests configurable: security.rate-limit.max-requests
(default: 1000)
- Updated RateLimitResetScheduler to use @Scheduled(cron =
"${security.rate-limit.reset-schedule:0 0 0 * * MON}")
(RateLimitResetScheduler.java:16)
- Updated SecurityConfiguration.rateLimitingFilter() to use configured
value (SecurityConfiguration.java:377)

  ---
- Enable access without security features

  Backend:
- Added /api/v1/config to permitAll endpoints
(SecurityConfiguration.java:261)
- Config endpoint already returns enableLogin status
(ConfigController.java:60)

  Frontend:
- AuthProvider now checks enableLogin before attempting JWT validation
(UseSession.tsx:98-112)
- If enableLogin=false, skips authentication entirely and sets
session=null
- Landing component bypasses auth check when enableLogin=false
(Landing.tsx:42-46)
- Added createAnonymousUser() and createAnonymousSession() utilities
(springAuthClient.ts:440-464)

Closes #3046
---

## Checklist

### General

- [x] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [x] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md)
(if applicable)
- [x] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md)
(if applicable)
- [x] I have performed a self-review of my own code
- [x] My changes generate no new warnings

### Documentation

- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [x] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md#6-testing)
for more details.

---------

Signed-off-by: dependabot[bot] <[email protected]>
Signed-off-by: stirlingbot[bot] <stirlingbot[bot]@users.noreply.github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Ludy <[email protected]>
Co-authored-by: EthanHealy01 <[email protected]>
Co-authored-by: Ethan <[email protected]>
Co-authored-by: Anthony Stirling <[email protected]>
Co-authored-by: stirlingbot[bot] <195170888+stirlingbot[bot]@users.noreply.github.com>

frontend/public/Login/github.svg

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