feat: Add Single Sign On(SSO) support

[GHkrishna]

Prerequisites

• Familiarity with current CREDEBL backend structure
• Understanding of Keycloak integration and SSO flow

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Summary

Implement SSO-related changes for CREDEBL including support for multi-client credential handling, user registration, login, email verification, redirection updates, and exposing required APIs.

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Why this change?

• Support multi-client SSO scenarios
• Enable user registration, login, and email verification flows
• Ensure proper redirection with Keycloak
• Provide necessary APIs for client use

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Proposed Improvements

• Multi-client client credential handling in CREDEBL backend
• User registration
• User login
• Redirection/Keycloak changes

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Steps to Reproduce (Current Flow)

1. Attempt to use SSO in a multi-client context
2. User registration and login may be limited

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Current Behavior

• Limited or no multi-client support
• Missing registration and login flow

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Expected Behavior

• Full support for multi-client SSO
• Working registration, login, and email verification
• Proper Keycloak redirection

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Environment

CREDEBL Version: v2.0.1