[Integrate] Stellar Asset Interface (SAI) Wrapper

[ayomideadeniran]

Description

Wrap a native Stellar Asset (like USDC or XLM) into a Soroban contract to allow the lab to accept XLM payments for premium certificates.

Requirements

• Use the Soroban token interface to interact with SAC.
• Implement a payment_gateway function.
• Verify transfer completion before proceeding with contract logic.

Level

• Intermediate

Rules for Contributors

• Please add an ETA (no more than 2 days) when expressing interest.

[esthercodez1]

I'd like to work on this.

Approach:

• Implement a payment_gateway module that wraps the Stellar Asset Contract (SAC) via the Soroban token interface
• Expose a pay(from, amount, asset) function that calls token::Client::transfer() under the hood, verifying transfer completion before returning success
• Add balance check + authorization (from.require_auth()) to ensure callers control the paying address
• Storage: persist accepted asset addresses and payment records in persistent() storage with proper TTL bumps
• Include unit tests covering: successful XLM payment, insufficient balance rejection, unauthorized caller rejection, and multi-asset support (USDC + XLM)

ETA: 1 day

I've contributed to this repo before (PR #115 — issue #35) and have experience with Soroban token interfaces and SAC integration from work on Alien-Gateway.

[emmanuelist]

@emmanuelist has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

I would like to work on this issue because I have hands-on experience with Soroban smart contracts and the Stellar SDK across multiple Wave contributions to this repo. I've worked with Soroban token interfaces, persistent/instance storage patterns, and cross-contract invocations in Rust. For this task, I'll implement the SAC wrapper using the soroban_sdk::token client, build a payment_gateway function that verifies transfer completion before proceeding, and include comprehensive tests covering payment success, insufficient balance, and invalid token scenarios.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @emmanuelist to this issue.