fix issue where auth emulator had invalid type for metadata.creation_time and metadata.last_sign_in_time

[aalej]

Description

Fixes #8109.

It seems like the expected type for user_record.metadata.creation_time and user_record.metadata.last_sign_in_time is number, since if they are sent to the functions emulator as a string, they can't be parsed https://github.com/firebase/firebase-functions/blob/5f7b331abd5a2a38a4e84de1e51411ea5919c0c3/src/common/providers/identity.ts#L554-L564

code below will result in Invalid Date

const creationTime = new Date("1769443209763").toUTCString()
console.log(creationTime) // Invalid Date

but numbers will work

const creationTime = new Date(1769443209763).toUTCString()
console.log(creationTime) // Mon, 26 Jan 2026 16:00:09 GMT

Seems like both firebase-functions and firebase-admin expect creation_time and last_sign_in_time to be numbers

• functions - https://github.com/firebase/firebase-functions/blob/11fcf3d48dd52bed00d3f651e0729059f2bf9a20/src/common/providers/identity.ts#L398
• admin - https://github.com/firebase/firebase-admin-node/blob/e2e5f0dc23c2bd138ac5bae0a36ac4a7ce4dc87d/src/auth/token-verifier.ts#L191

Scenarios Tested

See https://github.com/aalej/issues-8109_PR for a repro

Using the mcve:

1. Run firebase emulators:start --project demo-project
2. Go to "127.0.0.1:5000"
3. Add an email and password
4. Click "Create User" button
5. Check terminal logs where the emulator is running

{
  "providerData": [
    { "uid": "foo@bar.com", "email": "foo@bar.com", "providerId": "password" }
  ],
  "providerId": "password",
  "isNewUser": false,
  "metadata": {
    "creationTime": "Mon, 26 Jan 2026 17:15:21 GMT",
    "lastSignInTime": "Mon, 26 Jan 2026 17:15:21 GMT"
  }
}

matched with prod console logs

Sample Commands

[gemini-code-assist]

Summary of Changes

Hello @aalej, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical data type mismatch in the Firebase Auth Emulator. Previously, user metadata timestamps (creation_time and last_sign_in_time) were incorrectly provided as strings, leading to parsing failures in dependent Firebase services like Functions and Admin SDK. The changes ensure these timestamps are consistently represented as numbers, resolving compatibility issues and improving the reliability of user authentication events.

Highlights

• Data Type Correction: The metadata.creation_time and metadata.last_sign_in_time fields within the Auth Emulator's AuthBlockingEvent JWT payload are now correctly typed as number (timestamps in milliseconds) instead of string.
• Timestamp Parsing: Implemented parseInt() calls to convert string-based timestamps (user.lastLoginAt, user.createdAt) into numerical values before they are included in the JWT payload.
• Type Definition Update: The BlockingFunctionsJwtPayload TypeScript interface has been updated to reflect the correct number type for last_sign_in_time and creation_time metadata fields.
• Test Suite Alignment: Existing test cases in emailLink.spec.ts were updated to assert that creation_time is a number, aligning tests with the corrected data type.

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[gemini-code-assist]

Code Review

The pull request effectively addresses the issue where metadata.creation_time and metadata.last_sign_in_time were incorrectly formatted as strings instead of numbers in the Auth emulator's JWT payload. The changes correctly update the BlockingFunctionsJwtPayload type definition and ensure that these timestamp fields are parsed to numbers before being included in the JWT. The corresponding test assertions have also been updated to reflect this change, ensuring the emulator's behavior aligns with the expectations of firebase-functions and firebase-admin.