aws/session: Add support for assuming role via Web Identity Tokens (#…

…2667)

Adds support for assuming an role via the Web Identity Token. Allows for OIDC token files to be used by specifying the token path through the AWS_WEB_IDENTITY_TOKEN_FILE, and AWS_ROLE_ARN environment variables.

Replaces PR #2193

CHANGELOG_PENDING.md

@@ -1,4 +1,6 @@
 ### SDK Features
+* `aws/session`: Add support for assuming role via Web Identity Token ([#2667](https://github.com/aws/aws-sdk-go/pull/2667))
+  * Adds support for assuming an role via the Web Identity Token. Allows for OIDC token files to be used by specifying the token path through the AWS_WEB_IDENTITY_TOKEN_FILE, and AWS_ROLE_ARN environment variables.
 
 ### SDK Enhancements
 

aws/credentials/credentials.go

@@ -84,6 +84,12 @@ type Value struct {
 	ProviderName string
 }
 
+// HasKeys returns if the credentials Value has both AccessKeyID and
+// SecretAccessKey value set.
+func (v Value) HasKeys() bool {
+	return len(v.AccessKeyID) != 0 && len(v.SecretAccessKey) != 0
+}
+
 // A Provider is the interface for any component which will provide credentials
 // Value. A provider is required to manage its own Expired state, and what to
 // be expired means.

aws/credentials/stscreds/testdata/token.jwt

@@ -0,0 +1 @@
+foo

aws/credentials/stscreds/web_identity_provider.go

@@ -0,0 +1,99 @@
+package stscreds
+
+import (
+	"fmt"
+	"io/ioutil"
+	"strconv"
+	"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/sts"
+	"github.com/aws/aws-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 = func() time.Time {
+	return time.Now()
+}
+
+// WebIdentityRoleProvider is used to retrieve credentials using
+// an OIDC token.
+type WebIdentityRoleProvider struct {
+	credentials.Expiry
+
+	client       stsiface.STSAPI
+	ExpiryWindow time.Duration
+
+	tokenFilePath   string
+	roleARN         string
+	roleSessionName string
+}
+
+// NewWebIdentityCredentials will return a new set of credentials with a given
+// configuration, role arn, and token file path.
+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
+func NewWebIdentityRoleProvider(svc stsiface.STSAPI, roleARN, roleSessionName, path string) *WebIdentityRoleProvider {
+	return &WebIdentityRoleProvider{
+		client:          svc,
+		tokenFilePath:   path,
+		roleARN:         roleARN,
+		roleSessionName: roleSessionName,
+	}
+}
+
+// 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) {
+	b, err := ioutil.ReadFile(p.tokenFilePath)
+	if err != nil {
+		errMsg := fmt.Sprintf("unable to read file at %s", p.tokenFilePath)
+		return credentials.Value{}, awserr.New(ErrCodeWebIdentity, errMsg, 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)
+	}
+	resp, err := p.client.AssumeRoleWithWebIdentity(&sts.AssumeRoleWithWebIdentityInput{
+		RoleArn:          &p.roleARN,
+		RoleSessionName:  &sessionName,
+		WebIdentityToken: aws.String(string(b)),
+	})
+	if 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
+}

aws/credentials/stscreds/web_identity_provider_test.go

@@ -0,0 +1,113 @@
+// +build go1.7
+
+package stscreds
+
+import (
+	"fmt"
+	"reflect"
+	"testing"
+	"time"
+
+	"github.com/aws/aws-sdk-go/aws"
+	"github.com/aws/aws-sdk-go/aws/credentials"
+	"github.com/aws/aws-sdk-go/service/sts"
+)
+
+type mockSTS struct {
+	*sts.STS
+	AssumeRoleWithWebIdentityFn func(input *sts.AssumeRoleWithWebIdentityInput) (*sts.AssumeRoleWithWebIdentityOutput, error)
+}
+
+func (m *mockSTS) AssumeRoleWithWebIdentity(input *sts.AssumeRoleWithWebIdentityInput) (*sts.AssumeRoleWithWebIdentityOutput, error) {
+	if m.AssumeRoleWithWebIdentityFn != nil {
+		return m.AssumeRoleWithWebIdentityFn(input)
+	}
+
+	return nil, nil
+}
+
+func TestWebIdentityProviderRetrieve(t *testing.T) {
+	now = func() time.Time {
+		return time.Time{}
+	}
+
+	cases := []struct {
+		name              string
+		mockSTS           *mockSTS
+		roleARN           string
+		tokenFilepath     string
+		sessionName       string
+		expectedError     error
+		expectedCredValue credentials.Value
+	}{
+		{
+			name:          "session name case",
+			roleARN:       "arn",
+			tokenFilepath: "testdata/token.jwt",
+			sessionName:   "foo",
+			mockSTS: &mockSTS{
+				AssumeRoleWithWebIdentityFn: func(input *sts.AssumeRoleWithWebIdentityInput) (*sts.AssumeRoleWithWebIdentityOutput, error) {
+					if e, a := "foo", *input.RoleSessionName; !reflect.DeepEqual(e, a) {
+						t.Errorf("expected %v, but received %v", e, a)
+					}
+
+					return &sts.AssumeRoleWithWebIdentityOutput{
+						Credentials: &sts.Credentials{
+							Expiration:      aws.Time(time.Now()),
+							AccessKeyId:     aws.String("access-key-id"),
+							SecretAccessKey: aws.String("secret-access-key"),
+							SessionToken:    aws.String("session-token"),
+						},
+					}, nil
+				},
+			},
+			expectedCredValue: credentials.Value{
+				AccessKeyID:     "access-key-id",
+				SecretAccessKey: "secret-access-key",
+				SessionToken:    "session-token",
+				ProviderName:    WebIdentityProviderName,
+			},
+		},
+		{
+			name:          "valid case",
+			roleARN:       "arn",
+			tokenFilepath: "testdata/token.jwt",
+			mockSTS: &mockSTS{
+				AssumeRoleWithWebIdentityFn: func(input *sts.AssumeRoleWithWebIdentityInput) (*sts.AssumeRoleWithWebIdentityOutput, error) {
+					if e, a := fmt.Sprintf("%d", now().UnixNano()), *input.RoleSessionName; !reflect.DeepEqual(e, a) {
+						t.Errorf("expected %v, but received %v", e, a)
+					}
+
+					return &sts.AssumeRoleWithWebIdentityOutput{
+						Credentials: &sts.Credentials{
+							Expiration:      aws.Time(time.Now()),
+							AccessKeyId:     aws.String("access-key-id"),
+							SecretAccessKey: aws.String("secret-access-key"),
+							SessionToken:    aws.String("session-token"),
+						},
+					}, nil
+				},
+			},
+			expectedCredValue: credentials.Value{
+				AccessKeyID:     "access-key-id",
+				SecretAccessKey: "secret-access-key",
+				SessionToken:    "session-token",
+				ProviderName:    WebIdentityProviderName,
+			},
+		},
+	}
+
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			p := NewWebIdentityRoleProvider(c.mockSTS, c.roleARN, c.sessionName, c.tokenFilepath)
+			credValue, err := p.Retrieve()
+			if e, a := c.expectedError, err; !reflect.DeepEqual(e, a) {
+				t.Errorf("expected %v, but received %v", e, a)
+			}
+
+			if e, a := c.expectedCredValue, credValue; !reflect.DeepEqual(e, a) {
+				t.Errorf("expected %v, but received %v", e, a)
+			}
+		})
+	}
+}