You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: client.go
    path of file: ./repos/sliver/vendor/github.com/aws/aws-sdk-go-v2/credentials/endpointcreds/internal/client
    
    the code of the file until where you have to start completion: package client

import (
	"context"
	"fmt"
	"net/http"
	"time"

	"github.com/aws/aws-sdk-go-v2/aws"
	"github.com/aws/aws-sdk-go-v2/aws/middleware"
	"github.com/aws/aws-sdk-go-v2/aws/retry"
	awshttp "github.com/aws/aws-sdk-go-v2/aws/transport/http"
	"github.com/aws/smithy-go"
	smithymiddleware "github.com/aws/smithy-go/middleware"
	smithyhttp "github.com/aws/smithy-go/transport/http"
)

// ServiceID is the client identifer
const ServiceID = "endpoint-credentials"

// HTTPClient is a client for sending HTTP requests
type HTTPClient interface {
	Do(*http.Request) (*http.Response, error)
}

// Options is the endpoint client configurable options
type Options struct {
	// The endpoint to retrieve credentials from
	Endpoint string

	// The HTTP client to invoke API calls with. Defaults to client's default HTTP
	// implementation if nil.
	HTTPClient HTTPClient

	// Retryer guides how HTTP requests 
    
func (c *Client) GetCredentials(ctx context.Context, params *GetCredentialsInput, optFns ...func(*Options)) (*GetCredentialsOutput, error) {
	stack := smithymiddleware.NewStack("GetCredentials", smithyhttp.NewStackRequest)
	options := c.options.Copy()
	for _, fn := range optFns {
		fn(&options)
	}

	stack.Serialize.Add(&serializeOpGetCredential{}, smithymiddleware.After)
	stack.Build.Add(&buildEndpoint{Endpoint: options.Endpoint}, smithymiddleware.After)
	stack.Deserialize.Add(&deserializeOpGetCredential{}, smithymiddleware.After)
	retry.AddRetryMiddlewares(stack, retry.AddRetryMiddlewaresOptions{Retryer: options.Retryer})
	middleware.AddSDKAgentKey(middleware.FeatureMetadata, ServiceID)
	smithyhttp.AddErrorCloseResponseBodyMiddleware(stack)
	smithyhttp.AddCloseResponseBodyMiddleware(stack)

	for _, fn := range options.APIOptions {
		if err := fn(stack); err != nil {
			return nil, err
		}
	}

	handler := smithymiddleware.DecorateHandler(smithyhttp.NewClientHandler(options.HTTPClient), stack)
	result, _, err := handler.Handle(ctx, params)
	if err != nil {
		return nil, err
	}

	return result.(*GetCredentialsOutput), err
}