AWS Web Identity auth support

Signed-off-by: mateusz-ciesielski <mateusz.j.ciesielski@intel.com>

Author: mateusz-ciesielski

aws/credentials/stscreds/testdata/token.jwt

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+foo

aws/credentials/stscreds/web_identity_provider.go

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+package stscreds
+
+import (
+	"fmt"
+	"io/ioutil"
+	"strconv"
+	"time"
+
+	"github.com/IBM/ibm-cos-sdk-go/aws"
+	"github.com/IBM/ibm-cos-sdk-go/aws/awserr"
+	"github.com/IBM/ibm-cos-sdk-go/aws/client"
+	"github.com/IBM/ibm-cos-sdk-go/aws/credentials"
+	"github.com/IBM/ibm-cos-sdk-go/service/sts"
+	"github.com/IBM/ibm-cos-sdk-go/service/sts/stsiface"
+)
+
+const (
+	// ErrCodeWebIdentity will be used as an error code when constructing
+	// a new error to be returned during session creation or retrieval.
+	ErrCodeWebIdentity = "WebIdentityErr"
+
+	// WebIdentityProviderName is the web identity provider name
+	WebIdentityProviderName = "WebIdentityCredentials"
+)
+
+// now is used to return a time.Time object representing
+// the current time. This can be used to easily test and
+// compare test values.
+var now = time.Now
+
+// TokenFetcher should return WebIdentity token bytes or an error
+type TokenFetcher interface {
+	FetchToken(credentials.Context) ([]byte, error)
+}
+
+// FetchTokenPath is a path to a WebIdentity token file
+type FetchTokenPath string
+
+// FetchToken returns a token by reading from the filesystem
+func (f FetchTokenPath) FetchToken(ctx credentials.Context) ([]byte, error) {
+	data, err := ioutil.ReadFile(string(f))
+	if err != nil {
+		errMsg := fmt.Sprintf("unable to read file at %s", f)
+		return nil, awserr.New(ErrCodeWebIdentity, errMsg, err)
+	}
+	return data, nil
+}
+
+// WebIdentityRoleProvider is used to retrieve credentials using
+// an OIDC token.
+type WebIdentityRoleProvider struct {
+	credentials.Expiry
+
+	// The policy ARNs to use with the web identity assumed role.
+	PolicyArns []*sts.PolicyDescriptorType
+
+	// Duration the STS credentials will be valid for. Truncated to seconds.
+	// If unset, the assumed role will use AssumeRoleWithWebIdentity's default
+	// expiry duration. See
+	// https://docs.aws.amazon.com/sdk-for-go/api/service/sts/#STS.AssumeRoleWithWebIdentity
+	// for more information.
+	Duration time.Duration
+
+	// The amount of time the credentials will be refreshed before they expire.
+	// This is useful refresh credentials before they expire to reduce risk of
+	// using credentials as they expire. If unset, will default to no expiry
+	// window.
+	ExpiryWindow time.Duration
+
+	client stsiface.STSAPI
+
+	tokenFetcher    TokenFetcher
+	roleARN         string
+	roleSessionName string
+}
+
+// NewWebIdentityCredentials will return a new set of credentials with a given
+// configuration, role arn, and token file path.
+//
+// Deprecated: Use NewWebIdentityRoleProviderWithOptions for flexible
+// functional options, and wrap with credentials.NewCredentials helper.
+func NewWebIdentityCredentials(c client.ConfigProvider, roleARN, roleSessionName, path string) *credentials.Credentials {
+	svc := sts.New(c)
+	p := NewWebIdentityRoleProvider(svc, roleARN, roleSessionName, path)
+	return credentials.NewCredentials(p)
+}
+
+// NewWebIdentityRoleProvider will return a new WebIdentityRoleProvider with the
+// provided stsiface.STSAPI
+//
+// Deprecated: Use NewWebIdentityRoleProviderWithOptions for flexible
+// functional options.
+func NewWebIdentityRoleProvider(svc stsiface.STSAPI, roleARN, roleSessionName, path string) *WebIdentityRoleProvider {
+	return NewWebIdentityRoleProviderWithOptions(svc, roleARN, roleSessionName, FetchTokenPath(path))
+}
+
+// NewWebIdentityRoleProviderWithToken will return a new WebIdentityRoleProvider with the
+// provided stsiface.STSAPI and a TokenFetcher
+//
+// Deprecated: Use NewWebIdentityRoleProviderWithOptions for flexible
+// functional options.
+func NewWebIdentityRoleProviderWithToken(svc stsiface.STSAPI, roleARN, roleSessionName string, tokenFetcher TokenFetcher) *WebIdentityRoleProvider {
+	return NewWebIdentityRoleProviderWithOptions(svc, roleARN, roleSessionName, tokenFetcher)
+}
+
+// NewWebIdentityRoleProviderWithOptions will return an initialize
+// WebIdentityRoleProvider with the provided stsiface.STSAPI, role ARN, and a
+// TokenFetcher. Additional options can be provided as functional options.
+//
+// TokenFetcher is the implementation that will retrieve the JWT token from to
+// assume the role with. Use the provided FetchTokenPath implementation to
+// retrieve the JWT token using a file system path.
+func NewWebIdentityRoleProviderWithOptions(svc stsiface.STSAPI, roleARN, roleSessionName string, tokenFetcher TokenFetcher, optFns ...func(*WebIdentityRoleProvider)) *WebIdentityRoleProvider {
+	p := WebIdentityRoleProvider{
+		client:          svc,
+		tokenFetcher:    tokenFetcher,
+		roleARN:         roleARN,
+		roleSessionName: roleSessionName,
+	}
+
+	for _, fn := range optFns {
+		fn(&p)
+	}
+
+	return &p
+}
+
+// Retrieve will attempt to assume a role from a token which is located at
+// 'WebIdentityTokenFilePath' specified destination and if that is empty an
+// error will be returned.
+func (p *WebIdentityRoleProvider) Retrieve() (credentials.Value, error) {
+	return p.RetrieveWithContext(aws.BackgroundContext())
+}
+
+// RetrieveWithContext will attempt to assume a role from a token which is
+// located at 'WebIdentityTokenFilePath' specified destination and if that is
+// empty an error will be returned.
+func (p *WebIdentityRoleProvider) RetrieveWithContext(ctx credentials.Context) (credentials.Value, error) {
+	b, err := p.tokenFetcher.FetchToken(ctx)
+	if err != nil {
+		return credentials.Value{}, awserr.New(ErrCodeWebIdentity, "failed fetching WebIdentity token: ", err)
+	}
+
+	sessionName := p.roleSessionName
+	if len(sessionName) == 0 {
+		// session name is used to uniquely identify a session. This simply
+		// uses unix time in nanoseconds to uniquely identify sessions.
+		sessionName = strconv.FormatInt(now().UnixNano(), 10)
+	}
+
+	var duration *int64
+	if p.Duration != 0 {
+		duration = aws.Int64(int64(p.Duration / time.Second))
+	}
+
+	req, resp := p.client.AssumeRoleWithWebIdentityRequest(&sts.AssumeRoleWithWebIdentityInput{
+		PolicyArns:       p.PolicyArns,
+		RoleArn:          &p.roleARN,
+		RoleSessionName:  &sessionName,
+		WebIdentityToken: aws.String(string(b)),
+		DurationSeconds:  duration,
+	})
+
+	req.SetContext(ctx)
+
+	// InvalidIdentityToken error is a temporary error that can occur
+	// when assuming an Role with a JWT web identity token.
+	req.RetryErrorCodes = append(req.RetryErrorCodes, sts.ErrCodeInvalidIdentityTokenException)
+	if err := req.Send(); err != nil {
+		return credentials.Value{}, awserr.New(ErrCodeWebIdentity, "failed to retrieve credentials", err)
+	}
+
+	p.SetExpiration(aws.TimeValue(resp.Credentials.Expiration), p.ExpiryWindow)
+
+	value := credentials.Value{
+		AccessKeyID:     aws.StringValue(resp.Credentials.AccessKeyId),
+		SecretAccessKey: aws.StringValue(resp.Credentials.SecretAccessKey),
+		SessionToken:    aws.StringValue(resp.Credentials.SessionToken),
+		ProviderName:    WebIdentityProviderName,
+	}
+	return value, nil
+}