AWS Single Sign-On (SSO) Provider Support (aws#3755)

* Implement SSO Provider Support
* Implement Credential Chain Support for SSO Provider

aws/credentials/ssocreds/doc.go

@@ -0,0 +1,60 @@
+// Package ssocreds provides a credential provider for retrieving temporary AWS credentials using an SSO access token.
+//
+// IMPORTANT: The provider in this package does not initiate or perform the AWS SSO login flow. The SDK provider
+// expects that you have already performed the SSO login flow using AWS CLI using the "aws sso login" command, or by
+// some other mechanism. The provider must find a valid non-expired access token for the AWS SSO user portal URL in
+// ~/.aws/sso/cache. If a cached token is not found, it is expired, or the file is malformed an error will be returned.
+//
+// Loading AWS SSO credentials with the AWS shared configuration file
+//
+// You can use configure AWS SSO credentials from the AWS shared configuration file by
+// providing the specifying the required keys in the profile:
+//
+//  sso_account_id
+//  sso_region
+//  sso_role_name
+//  sso_start_url
+//
+// For example, the following defines a profile "devsso" and specifies the AWS SSO parameters that defines the target
+// account, role, sign-on portal, and the region where the user portal is located. Note: all SSO arguments must be
+// provided, or an error will be returned.
+//
+//  [profile devsso]
+//  sso_start_url = https://my-sso-portal.awsapps.com/start
+//  sso_role_name = SSOReadOnlyRole
+//  sso_region = us-east-1
+//  sso_account_id = 123456789012
+//
+// Using the config module, you can load the AWS SDK shared configuration, and specify that this profile be used to
+// retrieve credentials. For example:
+//
+//  sess, err := session.NewSessionWithOptions(session.Options{
+//      SharedConfigState: session.SharedConfigEnable,
+//      Profile:           "devsso",
+//  })
+//  if err != nil {
+//      return err
+//  }
+//
+// Programmatically loading AWS SSO credentials directly
+//
+// You can programmatically construct the AWS SSO Provider in your application, and provide the necessary information
+// to load and retrieve temporary credentials using an access token from ~/.aws/sso/cache.
+//
+//  svc := sso.New(sess, &aws.Config{
+//      Region: aws.String("us-west-2"), // Client Region must correspond to the AWS SSO user portal region
+//  })
+//
+//  provider := ssocreds.NewCredentialsWithClient(svc, "123456789012", "SSOReadOnlyRole", "https://my-sso-portal.awsapps.com/start")
+//
+//  credentials, err := provider.Get()
+//  if err != nil {
+//      return err
+//  }
+//
+// Additional Resources
+//
+// Configuring the AWS CLI to use AWS Single Sign-On: https://docs.aws.amazon.com/cli/latest/userguide/cli-configure-sso.html
+//
+// AWS Single Sign-On User Guide: https://docs.aws.amazon.com/singlesignon/latest/userguide/what-is.html
+package ssocreds

aws/credentials/ssocreds/os.go

@@ -0,0 +1,9 @@
+// +build !windows
+
+package ssocreds
+
+import "os"
+
+func getHomeDirectory() string {
+	return os.Getenv("HOME")
+}

aws/credentials/ssocreds/os_windows.go

@@ -0,0 +1,7 @@
+package ssocreds
+
+import "os"
+
+func getHomeDirectory() string {
+	return os.Getenv("USERPROFILE")
+}

aws/credentials/ssocreds/provider.go

@@ -0,0 +1,180 @@
+package ssocreds
+
+import (
+	"crypto/sha1"
+	"encoding/hex"
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"path/filepath"
+	"strings"
+	"time"
+
+	"github.com/aws/aws-sdk-go/aws"
+	"github.com/aws/aws-sdk-go/aws/awserr"
+	"github.com/aws/aws-sdk-go/aws/client"
+	"github.com/aws/aws-sdk-go/aws/credentials"
+	"github.com/aws/aws-sdk-go/service/sso"
+	"github.com/aws/aws-sdk-go/service/sso/ssoiface"
+)
+
+// ErrCodeSSOProviderInvalidToken is the code type that is returned if loaded token has expired or is otherwise invalid.
+// To refresh the SSO session run aws sso login with the corresponding profile.
+const ErrCodeSSOProviderInvalidToken = "SSOProviderInvalidToken"
+
+const invalidTokenMessage = "the SSO session has expired or is invalid"
+
+func init() {
+	nowTime = time.Now
+	defaultCacheLocation = defaultCacheLocationImpl
+}
+
+var nowTime func() time.Time
+
+// ProviderName is the name of the provider used to specify the source of credentials.
+const ProviderName = "SSOProvider"
+
+var defaultCacheLocation func() string
+
+func defaultCacheLocationImpl() string {
+	return filepath.Join(getHomeDirectory(), ".aws", "sso", "cache")
+}
+
+// Provider is an AWS credential provider that retrieves temporary AWS credentials by exchanging an SSO login token.
+type Provider struct {
+	credentials.Expiry
+
+	// The Client which is configured for the AWS Region where the AWS SSO user portal is located.
+	Client ssoiface.SSOAPI
+
+	// The AWS account that is assigned to the user.
+	AccountID string
+
+	// The role name that is assigned to the user.
+	RoleName string
+
+	// The URL that points to the organization's AWS Single Sign-On (AWS SSO) user portal.
+	StartURL string
+}
+
+// NewCredentials returns a new AWS Single Sign-On (AWS SSO) credential provider. The ConfigProvider is expected to be configured
+// for the AWS Region where the AWS SSO user portal is located.
+func NewCredentials(configProvider client.ConfigProvider, accountID, roleName, startURL string, optFns ...func(provider *Provider)) *credentials.Credentials {
+	return NewCredentialsWithClient(sso.New(configProvider), accountID, roleName, startURL, optFns...)
+}
+
+// NewCredentialsWithClient returns a new AWS Single Sign-On (AWS SSO) credential provider. The provided client is expected to be configured
+// for the AWS Region where the AWS SSO user portal is located.
+func NewCredentialsWithClient(client ssoiface.SSOAPI, accountID, roleName, startURL string, optFns ...func(provider *Provider)) *credentials.Credentials {
+	p := &Provider{
+		Client:    client,
+		AccountID: accountID,
+		RoleName:  roleName,
+		StartURL:  startURL,
+	}
+
+	for _, fn := range optFns {
+		fn(p)
+	}
+
+	return credentials.NewCredentials(p)
+}
+
+// Retrieve retrieves temporary AWS credentials from the configured Amazon Single Sign-On (AWS SSO) user portal
+// by exchanging the accessToken present in ~/.aws/sso/cache.
+func (p *Provider) Retrieve() (credentials.Value, error) {
+	return p.RetrieveWithContext(aws.BackgroundContext())
+}
+
+// RetrieveWithContext retrieves temporary AWS credentials from the configured Amazon Single Sign-On (AWS SSO) user portal
+// by exchanging the accessToken present in ~/.aws/sso/cache.
+func (p *Provider) RetrieveWithContext(ctx credentials.Context) (credentials.Value, error) {
+	tokenFile, err := loadTokenFile(p.StartURL)
+	if err != nil {
+		return credentials.Value{}, err
+	}
+
+	output, err := p.Client.GetRoleCredentialsWithContext(ctx, &sso.GetRoleCredentialsInput{
+		AccessToken: &tokenFile.AccessToken,
+		AccountId:   &p.AccountID,
+		RoleName:    &p.RoleName,
+	})
+	if err != nil {
+		return credentials.Value{}, err
+	}
+
+	expireTime := time.Unix(0, aws.Int64Value(output.RoleCredentials.Expiration)*int64(time.Millisecond)).UTC()
+	p.SetExpiration(expireTime, 0)
+
+	return credentials.Value{
+		AccessKeyID:     aws.StringValue(output.RoleCredentials.AccessKeyId),
+		SecretAccessKey: aws.StringValue(output.RoleCredentials.SecretAccessKey),
+		SessionToken:    aws.StringValue(output.RoleCredentials.SessionToken),
+		ProviderName:    ProviderName,
+	}, nil
+}
+
+func getCacheFileName(url string) (string, error) {
+	hash := sha1.New()
+	_, err := hash.Write([]byte(url))
+	if err != nil {
+		return "", err
+	}
+	return strings.ToLower(hex.EncodeToString(hash.Sum(nil))) + ".json", nil
+}
+
+type rfc3339 time.Time
+
+func (r *rfc3339) UnmarshalJSON(bytes []byte) error {
+	var value string
+
+	if err := json.Unmarshal(bytes, &value); err != nil {
+		return err
+	}
+
+	parse, err := time.Parse(time.RFC3339, value)
+	if err != nil {
+		return fmt.Errorf("expected RFC3339 timestamp: %v", err)
+	}
+
+	*r = rfc3339(parse)
+
+	return nil
+}
+
+type token struct {
+	AccessToken string  `json:"accessToken"`
+	ExpiresAt   rfc3339 `json:"expiresAt"`
+	Region      string  `json:"region,omitempty"`
+	StartURL    string  `json:"startUrl,omitempty"`
+}
+
+func (t token) Expired() bool {
+	return nowTime().Round(0).After(time.Time(t.ExpiresAt))
+}
+
+func loadTokenFile(startURL string) (t token, err error) {
+	key, err := getCacheFileName(startURL)
+	if err != nil {
+		return token{}, awserr.New(ErrCodeSSOProviderInvalidToken, invalidTokenMessage, err)
+	}
+
+	fileBytes, err := ioutil.ReadFile(filepath.Join(defaultCacheLocation(), key))
+	if err != nil {
+		return token{}, awserr.New(ErrCodeSSOProviderInvalidToken, invalidTokenMessage, err)
+	}
+
+	if err := json.Unmarshal(fileBytes, &t); err != nil {
+		return token{}, awserr.New(ErrCodeSSOProviderInvalidToken, invalidTokenMessage, err)
+	}
+
+	if len(t.AccessToken) == 0 {
+		return token{}, awserr.New(ErrCodeSSOProviderInvalidToken, invalidTokenMessage, nil)
+	}
+
+	if t.Expired() {
+		return token{}, awserr.New(ErrCodeSSOProviderInvalidToken, invalidTokenMessage, nil)
+	}
+
+	return t, nil
+}