feat: add shared decks and multi-account Mastodon OAuth

src/features/connections/credentials.server.ts

@@ -0,0 +1,97 @@
+import {
+  createCipheriv,
+  createDecipheriv,
+  createHash,
+  randomBytes,
+} from 'node:crypto'
+import { readFileSync } from 'node:fs'
+import { z } from 'zod'
+
+const envelopeSchema = z
+  .object({
+    version: z.literal(1),
+    keyId: z.string(),
+    iv: z.string(),
+    tag: z.string(),
+    ciphertext: z.string(),
+  })
+  .strict()
+
+function decodeBase64(value: string): Buffer {
+  const result = Buffer.from(value, 'base64')
+  if (result.toString('base64') !== value) throw new Error('Invalid encoding')
+  return result
+}
+
+function loadKey() {
+  const path = process.env.TWITTER_LITE_CREDENTIAL_KEY_FILE
+  if (!path) throw new Error('TWITTER_LITE_CREDENTIAL_KEY_FILE is required.')
+  let encoded: string
+  try {
+    encoded = readFileSync(path, 'utf8').trim()
+  } catch {
+    throw new Error('Could not read TWITTER_LITE_CREDENTIAL_KEY_FILE.')
+  }
+  let key: Buffer
+  try {
+    key = decodeBase64(encoded)
+    if (key.length !== 32) throw new Error('Invalid key length')
+  } catch {
+    throw new Error(
+      'TWITTER_LITE_CREDENTIAL_KEY_FILE must contain 32 random bytes encoded as base64.',
+    )
+  }
+  return {
+    key,
+    keyId: createHash('sha256').update(key).digest('hex').slice(0, 32),
+  }
+}
+
+function associatedData(context: string, keyId: string) {
+  if (!context) throw new Error('A credential record and purpose are required.')
+  return Buffer.from(
+    JSON.stringify(['twitter-lite-credential', 1, keyId, context]),
+  )
+}
+
+/** Context must identify both record and purpose; persist the returned opaque JSON. */
+export function encryptCredential(plaintext: string, context: string): string {
+  const { key, keyId } = loadKey()
+  const iv = randomBytes(12)
+  const cipher = createCipheriv('aes-256-gcm', key, iv)
+  cipher.setAAD(associatedData(context, keyId))
+  const ciphertext = Buffer.concat([
+    cipher.update(plaintext, 'utf8'),
+    cipher.final(),
+  ])
+  return JSON.stringify({
+    version: 1,
+    keyId,
+    iv: iv.toString('base64'),
+    tag: cipher.getAuthTag().toString('base64'),
+    ciphertext: ciphertext.toString('base64'),
+  })
+}
+
+export function decryptCredential(serialized: string, context: string): string {
+  const { key, keyId } = loadKey()
+  try {
+    const envelope = envelopeSchema.parse(JSON.parse(serialized))
+    if (envelope.keyId !== keyId) throw new Error('Different key')
+    const iv = decodeBase64(envelope.iv)
+    const tag = decodeBase64(envelope.tag)
+    if (iv.length !== 12 || tag.length !== 16)
+      throw new Error('Invalid envelope')
+    const decipher = createDecipheriv('aes-256-gcm', key, iv)
+    decipher.setAAD(associatedData(context, keyId))
+    decipher.setAuthTag(tag)
+    return Buffer.concat([
+      decipher.update(decodeBase64(envelope.ciphertext)),
+      decipher.final(),
+    ]).toString('utf8')
+  } catch {
+    throw new Error(
+      'Credential could not be decrypted. Check the stored credential and encryption key.',
+    )
+  }
+}