This page provides a quick introduction to HTTP Signatures PHP library and introductory examples.

If you have not already installed HTTP Signatures PHP library head over to the Installation page.

A reference signing client and verifying server are included that will actually exchange messages over HTTP. To see the library in actions, head over the the Reference Implementation Guide in the file REFERENCE.md.

Signing a message

Once you have a PSR-7 message ready to send, create a Context with:

  • your chosen algorithm
  • the list of headers to include in the signature
  • the key you will use to sign the message

For these examples we will sign the method + URI (indicated by (request-target) and the Content-Type header. This provides a very basic level of protection, and you should consider the headers you sign in your application carefully. These may also be specified by the verifier (most often a server hosting an API or web service).

Note also that this does not apply only to HTTP requests sent by a client. Servers can add a signature to responses that the client can verify.

Shared Secret Context (HMAC)

This type of signature uses a secret key known to you and the verifier.

use HttpSignatures\Context;

$context = new HttpSignatures\Context([
  'keys' => ['key12' => 'your-secret-here'],
  'algorithm' => 'hmac-sha256',
  'headers' => ['(request-target)', 'Content-Type'],

Private Key Context (RSA)

This type of signature uses a private key known only to you, which can be verified using a public key that is known to anyone who wants to verify the message.

The key file is assumed to be an unencrypted private key in PEM format.

use HttpSignatures\Context;

$context = new Context([
  'keys' => ['key43' => file_get_contents('/path/to/privatekeyfile')],
  'algorithm' => 'rsa-sha256',
  'headers' => ['(request-target)', 'Date', 'Accept'],

Signing the Message:


Now $message contains the Signature header:

// keyId="examplekey",algorithm="hmac-sha256",headers="...",signature="..."

Adding a Digest header while signing

Include a Digest header automatically when signing to also protect the payload (body) of the message in addition to the request-target and headers:

// SHA-256=<base64SHA256Digest>

Verifying a Signed Message

Most parameters are derived from the Signature in the signed message, so the Context can be created with fewer parameters.

It is probably most useful to create a Context with multilpe keys/certificates. the signature verifier will look up the key using the keyId attribute of the Signature header and use that to validate the signature.

Verifying a HMAC signed message

A message signed with an hmac signature is verified using the same key as the one used to sign the original message:

use HttpSignatures\Context;

$context = new HttpSignatures\Context([
  'keys' => ['key300' => 'some-other-secret',
              'key12' => 'secret-here']

$context->verifier()->isSigned($message); // true or false

Verifying a RSA signed message

An RSA signature is verified using the certificate associated with the Private Key that created the message. Create a context by importing the X.509 PEM format certificates in place of the ‘secret’:

use HttpSignatures\Context;

$context = new HttpSignatures\Context([
  'keys' => ['key43' => file_get_contents('/path/to/certificate'),
             'key87' => $someOtherCertificate],
$context->verifier()->isSigned($message); // true or false

Verifying a message digest

To confirm the body has a valid digest header and the header is a valid digest of the message body:

$context->verifier()->isValidDigest($message); // true or false

An all-in-one validation that the signature includes the digest, and the digest is valid for the message body:

$context->verifier()->isSignedWithDigest($message); // true or false

Symfony compatibility

Symfony requests normalize query strings which means the resulting request target can be incorrect. See https://github.com/symfony/psr-http-message-bridge/pull/30

When creating PSR-7 requests you use withRequestTarget to ensure the request target is correct. For example

use Symfony\Bridge\PsrHttpMessage\Factory\DiactorosFactory;
use Symfony\Component\HttpFoundation\Request;

$symfonyRequest = Request::create('/foo?b=1&a=2');
$psrRequest = (new DiactorosFactory())