How to use curl with CRT files

Secure connections may require CRT files to authenticate servers or clients. Providing the right CA certificate, client certificate, and private key ensures mutually trusted communication.

When public authorities are not applicable, custom CA certificates let cURL trust specific signers. Similarly, client certificates and keys authenticate the client side for restricted endpoints.

By configuring cURL with proper CRT, key, and CA files, secure connections remain robust in private, internal, or specialized environments, upholding encryption integrity and mutual authentication.

1. Determine if you need a client certificate, private key, or a CA certificate.

   Check server documentation or requirements.

2. Obtain the required CRT and key files from a trusted source.

   Keep these files secure and limit access to authorized personnel.

3. Provide the client certificate with --cert.

   $ curl --cert /path/to/client.crt "https://api.example.com"

   --cert supplies the client's certificate for verification.

4. Include the private key if needed with --key.

   $ curl --cert /path/to/client.crt --key /path/to/client.key "https://api.example.com"

   Matching certificate and key establish client identity.

5. Add a CA certificate with --cacert.

   $ curl --cacert /path/to/ca.crt "https://secure.example.com"

   --cacert trusts the specified CA for server validation.

6. Confirm the handshake completes without validation errors.

   If errors occur, verify paths, permissions, and certificate validity.