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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 = time.Now
// TokenFetcher shuold 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
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.
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 NewWebIdentityRoleProviderWithToken(svc, roleARN, roleSessionName, FetchTokenPath(path))
}
// NewWebIdentityRoleProviderWithToken will return a new WebIdentityRoleProvider with the
// provided stsiface.STSAPI and a TokenFetcher
func NewWebIdentityRoleProviderWithToken(svc stsiface.STSAPI, roleARN, roleSessionName string, tokenFetcher TokenFetcher) *WebIdentityRoleProvider {
return &WebIdentityRoleProvider{
client: svc,
tokenFetcher: tokenFetcher,
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) {
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
}
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