Why should you care?

Multi-tenant CRM RAG without filters could embed one customer's contract into another's answer.

See it live — copy this example

Paste into an ASP.NET Core 8+ / AgentNest project, then run with dotnet run (set your API keys in user-secrets).

// AgentNest.Security/ResponseRedactor.cs
public static class ResponseRedactor
{
    static readonly Regex Ssn = new(@"\b\d{3}-\d{2}-\d{4}\b");
    static readonly Regex Email = new(@"\b[\w.-]+@[\w.-]+\.\w+\b");
    public static string Redact(string text) =>
        Email.Replace(Ssn.Replace(text, "[REDACTED-SSN]"), "[REDACTED-EMAIL]");
}

What happened?

• ResponseRedactor strips SSN and email patterns from model output before JSON returns to CRM UI.
• Follow the steps below — typing the code yourself is the fastest way to learn.

Practice next

1. Redact outputs on hospital and CRM API responses.
2. Verify vector queries include mandatory tenantId predicate.
3. Scan prompts for API keys with secret scanner in CI.
4. Add credit card regex to ResponseRedactor.
5. Mask tenant B data in shared staging indexes.

Remember

Leakage defense: tenant filters, redaction, secret hygiene. Never mix tenant data in prompts or few-shot examples. Redact PII patterns in outbound model text.

Cross-tenant RAG incident

Bug omitted tenant filter; copilot cited wrong customer pricing.

Outcome: Mandatory tenant predicate plus redaction tests added to CI gate.