Architecture

StepFi is built across three repositories that work together as one protocol.

System Overview

StepFi-App (React Native + Expo)
        |
        | REST + JWT
        v
StepFi-API (NestJS + Fastify)
   |                    |
   | Unsigned XDR        | SQL queries
   v                    v
Soroban Contracts      Supabase (PostgreSQL)
(Stellar Ledger)             |
   |                    | Cache
   |              Redis (Upstash)
   v
Stellar Horizon
(Transaction submit)

Repositories

StepFi-API

NestJS backend with Fastify adapter. Handles wallet authentication, unsigned XDR construction, and off-chain data storage.

• Runtime: Node.js 20
• Framework: NestJS v11 with Fastify
• Database: Supabase (PostgreSQL)
• Cache: Redis via Upstash
• Auth: Stellar wallet signatures plus JWT tokens
• Live: https://stepfi-api.onrender.com/api/v1/docs

StepFi-Contracts

5 Soroban smart contracts written in Rust, deployed on Stellar testnet.

• Language: Rust
• Runtime: Soroban WASM
• Network: Stellar Testnet
• Release: v1.0.0 with all WASM artifacts

StepFi-App

React Native mobile app built with Expo.

• Framework: React Native + Expo SDK 52
• Navigation: Expo Router
• State: Zustand
• Wallets: Freighter + Lobstr (WalletConnect v2)
• Build: EAS Build

Data Flow

Loan Application Flow

1. Learner connects wallet (Freighter or Lobstr)
2. App calls POST /api/v1/auth/nonce
3. Learner signs nonce with their wallet
4. App calls POST /api/v1/auth/verify with signed nonce
5. API verifies signature on Stellar network
6. API returns JWT access token + refresh token
7. Learner submits loan application
8. API builds unsigned XDR calling creditline.create_loan()
9. App prompts learner to sign XDR with their wallet
10. API submits signed XDR to Stellar Horizon
11. Transaction confirmed on ledger
12. Loan record created in Supabase