Implementing MCP at an AI-Native Bank: Securely Letting LLMs Initiate Transfers
Liminal_Finance · reddit · 2026-07-31
AI-native neobank Liminal released its MCP Server, allowing users to plug accounts into clients like Claude or ChatGPT, supporting over 30 tools including balance checks, FX conversions, and stock trading.
Core Engineering Challenge:
How to securely allow a third-party LLM client to initiate money movement without granting it the authority to complete one.
Solution: Two-Phase Write
- Reads: Return data normally.
- Writes: The gateway freezes the action and params server-side and returns a confirmation. The user must approve it in the Liminal app based on a summary rendered from a server-side template.
- Security Mechanism: The execution after approval relies on the stored frozen params rather than anything the client sends afterwards, ensuring "what you approve is exactly what runs." The authorization is single-use and expires in 10 minutes.
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