Adds a AwsSigningHttpClientFactory

[kimpepper]

Description

Adds a AwsSigningHttpClientFactory to simplify the creation of a signing HTTP client using the \OpenSearch\Aws\SigningClientDecorator.

Also updates auth guide.

Example usage:

$endpoint = 'https://search-example.us-west-2.es.amazonaws.com';

$symfonyClient = (new \OpenSearch\HttpClient\SymfonyHttpClientFactory()->create([
    'base_uri' => $endpoint, // required.
]);

Use the AwsSigningHttpClientFactory to create a signing HTTP client:

$signingHttpClient = (new \OpenSearch\Aws\AwsSigningHttpClientFactory($symfonyClient))->create([
    'access_key' => '...', // optional. Will fallback to AWS SDK credential discovery.
    'secret_key' => '...', // optional. Will fallback to AWS SDK credential discovery.
    'base_uri' => $endpoint, // required for signing.
    'region' => 'us-west-2', // required for signing.
    'session_token' => '...', // optional.
    'service' => 'es', // optional. Allowed values are: 'es', 'aoss'. Defaults to 'es'.
  ],
]);

Issues Resolved

#257

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[dblock]

This looks like a very odd interface subclassing a client. In other clients Sigv4 is just a kind of auth that signs requests (adds headers), similar to basic auth. I think it should be something like this:

$endpoint = 'https://search-example.us-west-2.es.amazonaws.com';

$symfonyClient = (new \OpenSearch\HttpClient\SymfonyHttpClientFactory()->create([
    'base_uri' => $endpoint,
    'auth' => new \OpenSearch\Aws\AwsAuth(key, token, ...)
]);

AwsAuth would be something callable.

WDYT?

[kimpepper]

That would be specific to Symfony client. We'd need to do the same for Guzzle.

This is a decorator around any PSR Client.