x402 facilitator: implement GET /supported

[Miracle656]

Context

Lens is currently an x402 resource server — a seller. src/middleware/x402.ts builds an x402ResourceServer around an HTTPFacilitatorClient pointed at https://facilitator.stellar.org, and delegates both verify and settle to it.

We are going to implement the other side of that interface: a facilitator, served from Lens.

The contract is not guesswork — it is published and typed in @x402/core:

interface FacilitatorClient {
  verify(paymentPayload: PaymentPayload, paymentRequirements: PaymentRequirements): Promise<VerifyResponse>;
  settle(paymentPayload: PaymentPayload, paymentRequirements: PaymentRequirements): Promise<SettleResponse>;
  getSupported(): Promise<SupportedResponse>;
}

HTTPFacilitatorClient calls exactly three routes off its base URL: POST {url}/verify, POST {url}/settle, GET {url}/supported.

This issue: GET /supported

Start here because it moves no money and holds no keys — it is pure metadata, and it is the route every client hits first to decide whether we can serve them at all.

Return the payment kinds and extensions this facilitator supports, shaped as SupportedResponse from @x402/core. At minimum the exact scheme on Stellar, for both networks — the RFP requires mainnet and testnet, and Lens is already dual-network (docs/DUAL_NETWORK.md), so read the same config rather than inventing a second source of truth.

Where to look

• node_modules/@x402/core/dist/cjs/**/*.d.ts — SupportedResponse, PaymentPayload, PaymentRequirements are all typed there. Read them; do not infer the shape from blog posts.
• src/middleware/x402.ts — how Lens registers ExactStellarScheme today.
• The real https://facilitator.stellar.org/supported is live. Call it and match its shape.

Acceptance criteria

• GET /supported returns a valid SupportedResponse, type-checked against @x402/core rather than hand-rolled
• Both networks appear, driven by existing dual-network config
• Response matches the shape returned by facilitator.stellar.org/supported (include the comparison in the PR)
• Tests cover the response shape
• Route is not x402-gated — a facilitator cannot charge for its own capability discovery

Drips Wave · Complexity: Easy · 100 points

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[ChapmanOfWeb3]

@ChapmanOfWeb3 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi Maintainer, after reviewing the issue, I believe I have a good understanding of the problem and the expected solution. I’d appreciate the opportunity to work on it.

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[deshrajvermay9517-png]

@deshrajvermay9517-png has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi, I'd like to work on this. I'll implement GET /supported using @x402/core's SupportedResponse, use the existing dual-network config for testnet and mainnet, keep the route ungated, and add response-shape tests against the reference facilitator. Please assign it to me if it's available.

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[Elizabethxxx]

@Elizabethxxx has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi! I'd like to take on this issue. I'll implement the unauthenticated GET /supported route using the SupportedResponse type from @x402/core, derive both mainnet and testnet payment kinds from Lens's existing dual-network configuration, and align the response with the live Stellar facilitator's shape. I'll add tests for the response structure and network coverage, verify it is not x402-gated, and run the relevant type checks and test suite.

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

[dynamicwearsng-debug]

@dynamicwearsng-debug has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

i will like to work on this issues

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