Loan Origination System

A complete loan origination system built with Go, Temporal, and a simple SPA frontend. This system demonstrates human-in-the-loop workflows with Temporal signals for document verification, appraisal, and underwriting processes. All state is managed within Temporal workflows using queries for data retrieval.

Features

• Backend: Go with Gin framework
• Workflow Engine: Temporal for reliable, durable execution
• State Management: All data stored in Temporal workflow state (no database required)
• Frontend: Vanilla JavaScript SPA with role-based interface
• Human-in-the-Loop: Manual processes with signals for document verification and underwriting
• Queries: Temporal workflow queries for data retrieval

Architecture

The system includes 6 personas:

1. Loan Officer - Create loan applications
2. Customer - Upload documents
3. Loan Processor - Verify documents
4. Appraiser - Complete property appraisals
5. Underwriter - Make loan decisions
6. Fund Manager - Process funding

Prerequisites

• Go 1.21 or later
• Temporal CLI

Install the Temporal CLI from: https://docs.temporal.io/cli#installation

How to Run

1. Start Temporal Server

temporal server start-dev

2. Start the Temporal Worker (in another terminal)

go run cmd/worker/main.go

3. Start the API Server (in another terminal)

go run cmd/server/main.go

Open your browser and navigate to:

• Frontend: http://localhost:8082
• Temporal Web UI: http://localhost:8233

How to Use

Complete End-to-End Demo

1. Loan Officer:

   • Switch to "Loan Officer" role
   • Create a new loan application using the form
   • View your created applications

2. Customer:

   • Switch to "Customer" role
   • Upload documents for pending applications
   • Upload at least 2 documents (income statement, bank statement)

3. Loan Processor:

   • Switch to "Loan Processor" role
   • Verify uploaded documents by clicking "Verify Documents"
   • Approve or reject each document

4. Appraiser:

   • Switch to "Appraiser" role
   • Complete property appraisal for applications
   • Enter property value and notes
   • Trigger Credit score check API automatically. It will fail twice snd succeed 3rd time (simulated)

5. Underwriter:

   • Switch to "Underwriter" role
   • Review applications with completed appraisals
   • Make approve/reject decisions

6. Fund Manager:

   • Switch to "Fund Manager" role
   • Process funding for approved loans

Testing Third-Party Integration

You can simulate third-party document verification using curl:

# Get the loan ID and document ID from the frontend first
curl -X POST http://localhost:8082/api/v1/loans/{loan-id}/verify-documents \
  -H "Content-Type: application/json" \
  -d '{
    "document_id": "{document-id}",
    "verification_status": "verified",
    "verification_details": {
      "verified_by": "third-party-service",
      "confidence_score": 0.95
    }
  }'

API Endpoints

• POST /api/v1/loans - Create loan application
• GET /api/v1/loans - Get all loan applications
• GET /api/v1/loans/:id - Get specific loan application
• GET /api/v1/loans/:id/status - Get workflow status
• POST /api/v1/loans/:id/documents - Upload document
• POST /api/v1/loans/:id/verify-documents - Verify document
• POST /api/v1/loans/:id/appraisal - Complete appraisal
• POST /api/v1/loans/:id/underwriting - Make underwriting decision
• POST /api/v1/loans/:id/funding - Process funding

Temporal Features Demonstrated

• Long-running workflows - Loan origination process can take days/weeks
• Human-in-the-loop - Manual steps for document upload, verification, and underwriting
• Signal handling - External events trigger workflow progression
• Workflow state management - All data stored in workflow state
• Workflow queries - Real-time data retrieval from running workflows
• Timeout management - Workflows have timeouts for each step
• Workflow history - Complete audit trail of all actions