/**

* Nostr NIP-98 Authentication

*

* Implements HTTP authentication using Schnorr signatures as defined in:

* - NIP-98: https://nips.nostr.com/98

* - JIP-0001: https://github.com/JavaScriptSolidServer/jips/blob/main/jip-0001.md

*

* Authorization header format: "Nostr <base64-encoded-event>"

*

* The authenticated identity is returned as a did:nostr URI:

* did:nostr:<64-char-hex-pubkey>

*/

import { verifyEvent } from 'nostr-tools';

import crypto from 'crypto';

// NIP-98 event kind (references RFC 7235)

const HTTP_AUTH_KIND = 27235;

// Timestamp tolerance in seconds

const TIMESTAMP_TOLERANCE = 60;

/**

* Check if request has Nostr authentication

* @param {object} request - Fastify request object

* @returns {boolean}

*/

export function hasNostrAuth(request) {

const authHeader = request.headers.authorization;

return authHeader && authHeader.startsWith('Nostr ');

}

/**

* Extract token from Nostr authorization header

* @param {string} authHeader - Authorization header value

* @returns {string|null}

*/

export function extractNostrToken(authHeader) {

if (!authHeader || !authHeader.startsWith('Nostr ')) {

return null;

}

return authHeader.slice(6).trim();

}

/**

* Decode NIP-98 event from base64 token

* @param {string} token - Base64 encoded event

* @returns {object|null} Decoded event or null

*/

function decodeEvent(token) {

try {

const decoded = Buffer.from(token, 'base64').toString('utf8');

return JSON.parse(decoded);

} catch {

return null;

}

}

/**

* Get tag value from event

* @param {object} event - Nostr event

* @param {string} tagName - Tag name (e.g., 'u', 'method')

* @returns {string|null} Tag value or null

*/

function getTagValue(event, tagName) {

if (!event.tags || !Array.isArray(event.tags)) {

return null;

}

const tag = event.tags.find(t => Array.isArray(t) && t[0] === tagName);

return tag ? tag[1] : null;

}

/**

* Convert Nostr pubkey to did:nostr URI

* @param {string} pubkey - 64-char hex public key

* @returns {string} did:nostr URI

*/

export function pubkeyToDidNostr(pubkey) {

return `did:nostr:${pubkey.toLowerCase()}`;

}

/**

* Verify NIP-98 authentication and return agent identity

* @param {object} request - Fastify request object

* @returns {Promise<{webId: string|null, error: string|null}>}

*/

export async function verifyNostrAuth(request) {

const token = extractNostrToken(request.headers.authorization);

if (!token) {

return { webId: null, error: 'Missing Nostr token' };

}

// Decode the event

const event = decodeEvent(token);

if (!event) {

return { webId: null, error: 'Invalid token format: could not decode base64 JSON' };

}

// Validate event kind (must be 27235)

if (event.kind !== HTTP_AUTH_KIND) {

return { webId: null, error: `Invalid event kind: expected ${HTTP_AUTH_KIND}, got ${event.kind}` };

}

// Validate timestamp (within ±60 seconds)

const now = Math.floor(Date.now() / 1000);

const eventTime = event.created_at;

if (!eventTime || Math.abs(now - eventTime) > TIMESTAMP_TOLERANCE) {

return { webId: null, error: 'Event timestamp outside acceptable window (±60s)' };

}

// Build full URL for validation

const protocol = request.protocol || 'http';

const host = request.headers.host || request.hostname;

const fullUrl = `${protocol}://${host}${request.url}`;

// Validate URL tag matches request URL

const eventUrl = getTagValue(event, 'u');

if (!eventUrl) {

return { webId: null, error: 'Missing URL tag in event' };

}

// Compare URLs (normalize by removing trailing slashes)

const normalizedEventUrl = eventUrl.replace(/\/$/, '');

const normalizedRequestUrl = fullUrl.replace(/\/$/, '');

const normalizedRequestUrlNoQuery = fullUrl.split('?')[0].replace(/\/$/, '');

if (normalizedEventUrl !== normalizedRequestUrl && normalizedEventUrl !== normalizedRequestUrlNoQuery) {

return { webId: null, error: `URL mismatch: event URL "${eventUrl}" does not match request URL "${fullUrl}"` };

}

// Validate method tag matches request method

const eventMethod = getTagValue(event, 'method');

if (!eventMethod) {

return { webId: null, error: 'Missing method tag in event' };

}

if (eventMethod.toUpperCase() !== request.method.toUpperCase()) {

return { webId: null, error: `Method mismatch: expected ${request.method}, got ${eventMethod}` };

}

// Validate payload hash if present and request has body

const payloadTag = getTagValue(event, 'payload');

if (payloadTag && request.body) {

let bodyString;

if (typeof request.body === 'string') {

bodyString = request.body;

} else if (Buffer.isBuffer(request.body)) {

bodyString = request.body.toString();

} else {

bodyString = JSON.stringify(request.body);

}

const expectedHash = crypto.createHash('sha256').update(bodyString).digest('hex');

if (payloadTag.toLowerCase() !== expectedHash.toLowerCase()) {

return { webId: null, error: 'Payload hash mismatch' };

}

}

// Validate pubkey exists

if (!event.pubkey || typeof event.pubkey !== 'string' || event.pubkey.length !== 64) {

return { webId: null, error: 'Invalid or missing pubkey' };

}

// Verify Schnorr signature

const isValid = verifyEvent(event);

if (!isValid) {

return { webId: null, error: 'Invalid Schnorr signature' };

}

// Return did:nostr as the agent identifier

const didNostr = pubkeyToDidNostr(event.pubkey);

return { webId: didNostr, error: null };

}

/**

* Get Nostr pubkey from request if authenticated via NIP-98

* @param {object} request - Fastify request object

* @returns {Promise<string|null>} Hex pubkey or null

*/

export async function getNostrPubkey(request) {

if (!hasNostrAuth(request)) {

return null;

}

const token = extractNostrToken(request.headers.authorization);

if (!token) {

return null;

}

try {

const event = decodeEvent(token);

return event?.pubkey || null;

} catch {

return null;

}

}