feat: design pluggable authentication architecture (#455)

[Ceejaytech25]

Description

Resolves #455

This PR introduces a highly resilient, pluggable authentication architecture designed to seamlessly support multiple authentication mechanisms (OAuth, SAML, DID) while maintaining a unified identity model across the SoroTask platform.

🚀 Key Features & Architectural Changes

• Unified Identity Manager (IdentityManager.ts): Introduces a normalization layer that takes disparate identity profiles (OAuth subjects, SAML NameIDs, DID addresses) and maps them to our standardized User model with consistent roles and permission handling.
• Pluggable Auth Pipeline (AuthPipeline.ts): Built a fault-tolerant pipeline that acts as the entry point for authentication requests. It handles dynamic provider registration, request routing, and strict error tracking.
• Core Providers (providers/):
  • OAuthProvider: Foundation for standard OAuth2 integrations (Google, GitHub, etc.).
  • SAMLProvider: Foundation for enterprise Single Sign-On (SSO) integrations.
  • DIDProvider: Support for Web3/Stellar decentralized identities and cryptographic signatures.
• Strict Typings (types.ts): Fully typed interfaces for credentials, provider configurations, and authentication results to guarantee strict architectural boundaries.

🛠️ Fixes & Improvements

• Fixed a pre-existing syntax error in frontend/jest.config.js that was preventing test suites from running properly.

✅ Testing

• Unit tests written for the entire authentication pipeline, identity resolution, and all providers.
• Achieved >90% code coverage for the newly introduced src/lib/auth module.

📋 Reviewer Notes

This serves as the foundational backend infrastructure for our new authentication flows. It is currently designed to cleanly integrate into the existing NextAuth configuration or act as a standalone service interface moving forward.

Closes #455
Closes #456

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[Ceejaytech25]

@ayomideadeniran , pls review

[EDOHWARES]

@Ceejaytech25 , LGTM!