Fix: Handle self-signed certificates in PostgreSQL SSL connections

[scrobot]

Fix: Handle self-signed certificates in PostgreSQL SSL connections

Problem

When connecting to PostgreSQL databases with SSL enabled (particularly AWS RDS instances), the MCP server fails with the error:

MCP error -32603: self-signed certificate in certificate chain

This issue occurs because AWS RDS uses SSL certificates that may not be in the default trusted certificate store, and the node-postgres library fails to validate the certificate chain.

Solution

This PR implements a flexible solution for handling SSL connections in the PostgreSQL MCP server:

1. Conditional SSL Configuration: SSL settings are only applied when needed, based on the connection string parameters (sslmode=require, prefer, verify-ca, or verify-full).

2. Configurable Certificate Validation: Added support for the rejectUnauthorized parameter in the connection string to control certificate validation:

   • rejectUnauthorized=false: Disables certificate validation (needed for AWS RDS with self-signed certs)
   • rejectUnauthorized=true: Enforces certificate validation (default for security)

3. Improved Client Connections: Individual client connections now properly inherit SSL settings from the connection string.

Usage Examples

1. For AWS RDS with self-signed certificates:

postgresql://username:password@host:port/dbname?sslmode=require&rejectUnauthorized=false

2. For secure connections with certificate validation:

postgresql://username:password@host:port/dbname?sslmode=require&rejectUnauthorized=true

3. For non-SSL connections:

postgresql://username:password@host:port/dbname

Related Issues

Fixes #1047