* - api_provider: (callable) An optional PHP callable that accepts a
*   type, service, and version argument, and returns an array of
*   corresponding configuration data. The type value can be one of api,
*   waiter, or paginator.
* - configuration_mode:
*   (Aws\DefaultsMode\ConfigurationInterface|Aws\CacheInterface|string|closure)
*   Sets the default configuration mode. Otherwise provide an instance of
*   Aws\DefaultsMode\ConfigurationInterface, an instance of 
*   Aws\CacheInterface, or a string containing a valid mode
* - credentials:
*   (Aws\Credentials\CredentialsInterface|Aws\CacheInterface|array|bool|callable)
*   Specifies the credentials used to sign requests. Provide an
*   Aws\Credentials\CredentialsInterface object, an associative array of
*   "key", "secret", and an optional "token" key, `false` to use null
*   credentials, or a callable credentials provider used to create
*   credentials or return null. See Aws\Credentials\CredentialProvider for
*   a list of built-in credentials providers. If no credentials are
*   provided, the SDK will attempt to load them from the environment.
* - csm:
*   (Aws\ClientSideMonitoring\ConfigurationInterface|callable|array|bool)
*   CSM options for the client. Provides a callable wrapping a promise, a
*   boolean "false", an instance of ConfigurationInterface, or an
*   associative array of "enabled", "host", "port", and "client_id".
* - debug: (bool|array) Set to true to display debug information when
*   sending requests. Alternatively, you can provide an associative array
*   with the following keys: logfn: (callable) Function that is invoked
*   with log messages; stream_size: (int) When the size of a stream is
*   greater than this number, the stream data will not be logged (set to
*   "0" to not log any stream data); scrub_auth: (bool) Set to false to
*   disable the scrubbing of auth data from the logged messages; http:
*   (bool) Set to false to disable the "debug" feature of lower level HTTP
*   adapters (e.g., verbose curl output).
* - disable_host_prefix_injection: (bool, default=bool(false)) Set to
*   true to disable host prefix injection logic for services that use it.
*   This disables the entire prefix injection, including the portions
*   supplied by user-defined parameters. Setting this flag will have no
*   effect on services that do not use host prefix injection.
* - endpoint: (string) The full URI of the webservice. This is only
*   required when connecting to a custom endpoint (e.g., a local version
*   of S3).
* - endpoint_discovery:
*   (Aws\EndpointDiscovery\ConfigurationInterface|Aws\CacheInterface|array|callable)
*   Specifies settings for endpoint discovery. Provide an instance of
*   Aws\EndpointDiscovery\ConfigurationInterface, an instance
*   Aws\CacheInterface, a callable that provides a promise for a
*   Configuration object, or an associative array with the following keys:
*   enabled: (bool) Set to true to enable endpoint discovery, false to
*   explicitly disable it. Defaults to false; cache_limit: (int) The
*   maximum number of keys in the endpoints cache. Defaults to 1000.
* - endpoint_provider: (callable) An optional PHP callable that
*   accepts a hash of options including a "service" and "region" key and
*   returns NULL or a hash of endpoint data, of which the "endpoint" key
*   is required. See Aws\Endpoint\EndpointProvider for a list of built-in
*   providers.
* - handler: (callable) A handler that accepts a command object,
*   request object and returns a promise that is fulfilled with an
*   Aws\ResultInterface object or rejected with an
*   Aws\Exception\AwsException. A handler does not accept a next handler
*   as it is terminal and expected to fulfill a command. If no handler is
*   provided, a default Guzzle handler will be utilized.
* - http: (array, default=array(0)) Set to an array of SDK request
*   options to apply to each request (e.g., proxy, verify, etc.).
* - http_handler: (callable) An HTTP handler is a function that
*   accepts a PSR-7 request object and returns a promise that is fulfilled
*   with a PSR-7 response object or rejected with an array of exception
*   data. NOTE: This option supersedes any provided "handler" option.
* - idempotency_auto_fill: (bool|callable, default=bool(true)) Set to
*   false to disable SDK to populate parameters that enabled
*   'idempotencyToken' trait with a random UUID v4 value on your behalf.
*   Using default value 'true' still allows parameter value to be
*   overwritten when provided. Note: auto-fill only works when
*   cryptographically secure random bytes generator
*   functions(random_bytes, openssl_random_pseudo_bytes or
*   mcrypt_create_iv) can be found. You may also provide a callable source
*   of random bytes.
* - profile: (string) Allows you to specify which profile to use when
*   credentials are created from the AWS credentials file in your HOME
*   directory. This setting overrides the AWS_PROFILE environment
*   variable. Note: Specifying "profile" will cause the "credentials" and
*   "use_aws_shared_config_files" keys to be ignored.
* - region: (string, required) Region to connect to. See
*   http://docs.aws.amazon.com/general/latest/gr/rande.html for a list of
*   available regions.
* - retries:
*   (int|Aws\Retry\ConfigurationInterface|Aws\CacheInterface|callable|array)
*   Configures the retry mode and maximum number of allowed retries for a
*   client (pass 0 to disable retries). Provide an integer for 'legacy'
*   mode with the specified number of retries. Otherwise provide an
*   instance of Aws\Retry\ConfigurationInterface, an instance of 
*   Aws\CacheInterface, a callable function, or an array with the
*   following keys: mode: (string) Set to 'legacy', 'standard' (uses retry
*   quota management), or 'adapative' (an experimental mode that adds
*   client-side rate limiting to standard mode); max_attempts: (int) The
*   maximum number of attempts for a given request. 
* - scheme: (string, default=string(5) "https") URI scheme to use when
*   connecting connect. The SDK will utilize "https" endpoints (i.e.,
*   utilize SSL/TLS connections) by default. You can attempt to connect to
*   a service over an unencrypted "http" endpoint by setting ``scheme`` to
*   "http".
* - signature_provider: (callable) A callable that accepts a signature
*   version name (e.g., "v4"), a service name, and region, and  returns a
*   SignatureInterface object or null. This provider is used to create
*   signers utilized by the client. See Aws\Signature\SignatureProvider
*   for a list of built-in providers
* - signature_version: (string) A string representing a custom
*   signature version to use with a service (e.g., v4). Note that
*   per/operation signature version MAY override this requested signature
*   version.
* - signing_name: (string) A string representing a custom service name
*   to be used when calculating a request signature.
* - signing_region: (string) A string representing a custom region
*   name to be used when calculating a request signature.
* - stats: (bool|array, default=bool(false)) Set to true to gather
*   transfer statistics on requests sent. Alternatively, you can provide
*   an associative array with the following keys: retries: (bool) Set to
*   false to disable reporting on retries attempted; http: (bool) Set to
*   true to enable collecting statistics from lower level HTTP adapters
*   (e.g., values returned in GuzzleHttp\TransferStats). HTTP handlers
*   must support an http_stats_receiver option for this to have an effect;
*   timer: (bool) Set to true to enable a command timer that reports the
*   total wall clock time spent on an operation in seconds.
* - ua_append: (string|array, default=array(0)) Provide a string or
*   array of strings to send in the User-Agent header.
* - use_aws_shared_config_files: (bool, default=bool(true)) Set to
*   false to disable checking for shared aws config files usually located
*   in '~/.aws/config' and '~/.aws/credentials'.  This will be ignored if
*   you set the 'profile' setting.
* - use_dual_stack_endpoint:
*   (bool|Aws\Endpoint\UseDualstackEndpoint\Configuration|Aws\CacheInterface|callable)
*   Set to true to enable the use of dual-stack endpoints
* - use_fips_endpoint:
*   (bool|Aws\Endpoint\UseFipsEndpoint\Configuration|Aws\CacheInterface|callable)
*   Set to true to enable the use of FIPS pseudo regions
* - validate: (bool|array, default=bool(true)) Set to false to disable
*   client-side parameter validation. Set to true to utilize default
*   validation constraints. Set to an associative array of validation
*   options to enable specific validation constraints.
* - version: (string, required) The version of the webservice to
*   utilize (e.g., 2006-03-01).