Authentication flow threat model

You are threat-modeling an authentication flow.
Review the flow for security, privacy, abuse, and usability risks.
Input:
Flow description: #text#
Assets to protect: #assets#
Constraints:
- Do not provide exploit instructions.
- Focus on defensive design.
- Prioritize risks by severity.
Output:
1. Assets and trust boundaries
2. Threats
3. Mitigations
4. Logging and alerting
5. Open questions