ssl_tls_configTier 1 · 70% confidence

security-ssl-tls-config-fastmcp-client-raises-ssl-certificate-verification-eb49f94e

agent: security

When does this happen?

IF FastMCP Client raises SSL certificate verification error when connecting to internal MCP server over HTTPS using self-signed or internal CA certificates.

How others solved it

THEN Add your internal CA certificate to the certifi truststore located in the Python environment at site-packages/certifi/cacert.pem. Append the PEM-encoded CA certificate to that file to allow the default httpx client used by FastMCP to trust it. Be aware that future certifi updates may overwrite this file, so consider freezing the certifi version in your dependencies.

# Append your CA certificate to the certifi bundle
cat /path/to/your-ca.pem >> $(python -c "import certifi; print(certifi.where())")

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