Security Headers & CSP - AgentFront

Quick Start
CSP Configuration
Example Directives
Security Headers
Environment Variables
Programmatic Access
Report-Only Mode
Related

FrontMCP applies security headers to every HTTP response, including Content Security Policy (CSP), Strict-Transport-Security (HSTS), X-Frame-Options, and X-Content-Type-Options. Configure them via frontmcp.config server settings --- they are injected as environment variables at build time and read by the built-in middleware.

Quick Start

Add security headers to frontmcp.config.ts:

import { defineConfig } from '@frontmcp/cli';

export default defineConfig({
  name: 'my-server',
  deployments: [{
    target: 'node',
    server: {
      csp: {
        enabled: true,
        directives: "default-src 'self'; script-src 'self' https://cdn.example.com; upgrade-insecure-requests",
        reportOnly: false,
      },
      headers: {
        hsts: 'max-age=31536000; includeSubDomains',
        contentTypeOptions: 'nosniff',
        frameOptions: 'DENY',
      },
    },
  }],
});

Build and deploy --- headers are applied automatically on every response.

CSP Configuration

Field	Type	Default	Description
`enabled`	boolean	`false`	Enable CSP headers
`directives`	string	---	Semicolon-separated CSP directives
`reportUri`	string	---	URI for CSP violation reports
`reportOnly`	boolean	`false`	Use `Content-Security-Policy-Report-Only` instead of enforcement

Value-less CSP directives like upgrade-insecure-requests and block-all-mixed-content are supported. Separate them with semicolons like any other directive.

Example Directives

default-src 'self'; script-src 'self' https://cdn.example.com; style-src 'self' 'unsafe-inline'; img-src *; upgrade-insecure-requests

Security Headers

Header	Config Field	Default	Description
`Strict-Transport-Security`	`headers.hsts`	---	HSTS policy for HTTPS enforcement
`X-Content-Type-Options`	`headers.contentTypeOptions`	`nosniff`	Prevent MIME type sniffing
`X-Frame-Options`	`headers.frameOptions`	`DENY`	Clickjacking protection
Custom headers	`headers.custom`	---	Record of additional header name-value pairs

X-Content-Type-Options: nosniff and X-Frame-Options: DENY are applied by default even without explicit configuration. Set them to empty strings to disable.

Environment Variables

All settings are injected as environment variables at build time by the deployment adapter:

Variable	Maps To
`FRONTMCP_CSP_ENABLED`	`server.csp.enabled`
`FRONTMCP_CSP_DIRECTIVES`	`server.csp.directives`
`FRONTMCP_CSP_REPORT_URI`	`server.csp.reportUri`
`FRONTMCP_CSP_REPORT_ONLY`	`server.csp.reportOnly`
`FRONTMCP_HSTS`	`server.headers.hsts`
`FRONTMCP_CONTENT_TYPE_OPTIONS`	`server.headers.contentTypeOptions`
`FRONTMCP_FRAME_OPTIONS`	`server.headers.frameOptions`

You can override these at runtime without rebuilding:

FRONTMCP_CSP_ENABLED=1 \
FRONTMCP_CSP_DIRECTIVES="default-src 'none'" \
FRONTMCP_HSTS="max-age=0" \
node dist/main.js

Programmatic Access

For custom middleware or adapters, use the security header functions directly:

import {
  readCspFromEnv,
  buildCspHeaderValue,
  getCspHeaderName,
  readSecurityHeadersFromEnv,
  applySecurityHeaders,
} from '@frontmcp/sdk';

// Read configuration from environment
const csp = readCspFromEnv();
const headers = readSecurityHeadersFromEnv();

// Apply to a response
applySecurityHeaders(res, headers, csp);

// Or build the CSP header value manually
if (csp?.enabled) {
  const headerName = getCspHeaderName(csp.reportOnly); // 'Content-Security-Policy' or '...-Report-Only'
  const headerValue = buildCspHeaderValue(csp);
  res.setHeader(headerName, headerValue);
}

Report-Only Mode

Use reportOnly: true to test CSP rules without blocking content:

server: {
  csp: {
    enabled: true,
    directives: "default-src 'self'",
    reportUri: 'https://report.example.com/csp',
    reportOnly: true,  // violations are reported, not blocked
  },
}

This sets the Content-Security-Policy-Report-Only header instead of Content-Security-Policy, allowing you to monitor violations before enforcing the policy.

Configuration File

Full configuration reference

Production Build

Build and deploy for production

Transport Security