feat: add requestAttributes for signed user attributes

[sea-snake]

Adds a requestAttributes method to AuthClient that requests signed user attributes from the identity provider via the signer's JSON-RPC interface. Attributes can be requested in parallel with sign-in.

The method requires a canister-issued nonce to prevent replay attacks and bind attributes to a specific backend action. The signed attribute bundle also includes implicit:origin and implicit:issued_at_timestamp_ns for the backend canister to verify.

const authClient = new AuthClient();

const nonce: Uint8Array = await backend.registerBegin();
const signInPromise = authClient.signIn();
const attributesPromise = authClient.requestAttributes({ keys: ['email'], nonce });

await signInPromise;
const { data, signature } = await attributesPromise;

The method sends an ii-icrc3-attributes JSON-RPC request with the requested attribute keys and the provided nonce, and returns the base64-decoded data and signature as Uint8Array. Throws on error responses or invalid results.

Breaking changes

• AuthClient.login() is renamed to AuthClient.signIn().
• AuthClientLoginOptions is renamed to AuthClientSignInOptions.

---

Prev: #84

[Copilot]

Pull request overview

This pull request adds a requestAttributes method to AuthClient that enables requesting signed user attributes from the identity provider via a JSON-RPC interface. The method can be called during login or separately, allowing attributes like email and name to be requested and verified with cryptographic signatures.

Changes:

• Added requestAttributes method to AuthClient class for requesting signed user attributes with optional custom nonce
• Added SignedAttributes interface to represent the signed attribute response (data and signature as Uint8Array)
• Exported OPENID_PROVIDER_URLS constant to support documentation examples
• Implemented base64 encoding/decoding helper functions with fallback support for native Uint8Array methods
• Added comprehensive tests covering normal flow, custom nonce, random nonce generation, error handling, and validation
• Updated README and quick-start documentation with usage examples

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
src/client/auth-client.ts	Added requestAttributes method, SignedAttributes interface, and base64 helper functions; exported OPENID_PROVIDER_URLS
tests/client/auth-client.test.ts	Added mocking for sendRequest method and comprehensive tests for requestAttributes functionality
README.md	Added documentation section with usage examples for requesting user attributes
docs/src/content/docs/quick-start.md	Updated quick-start guide to show parallel login and attribute request pattern

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.