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aws.go
518 lines (438 loc) · 16.9 KB
/
aws.go
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// Copyright 2019 The OPA Authors. All rights reserved.
// Use of this source code is governed by an Apache2
// license that can be found in the LICENSE file.
package rest
import (
"bytes"
"encoding/json"
"encoding/xml"
"errors"
"fmt"
"io"
"net/http"
"net/url"
"os"
"path/filepath"
"strings"
"time"
"github.com/go-ini/ini"
"github.com/open-policy-agent/opa/internal/providers"
"github.com/open-policy-agent/opa/logging"
)
const (
// ref. https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/iam-roles-for-amazon-ec2.html
ec2DefaultCredServicePath = "http://169.254.169.254/latest/meta-data/iam/security-credentials/"
// ref. https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/configuring-instance-metadata-service.html
ec2DefaultTokenPath = "http://169.254.169.254/latest/api/token"
// ref. https://docs.aws.amazon.com/AmazonECS/latest/userguide/task-iam-roles.html
ecsDefaultCredServicePath = "http://169.254.170.2"
ecsRelativePathEnvVar = "AWS_CONTAINER_CREDENTIALS_RELATIVE_URI"
// ref. https://docs.aws.amazon.com/IAM/latest/UserGuide/id_credentials_temp_enable-regions.html
stsDefaultPath = "https://sts.amazonaws.com"
stsRegionPath = "https://sts.%s.amazonaws.com"
// ref. https://docs.aws.amazon.com/cli/latest/userguide/cli-configure-envvars.html
accessKeyEnvVar = "AWS_ACCESS_KEY_ID"
secretKeyEnvVar = "AWS_SECRET_ACCESS_KEY"
securityTokenEnvVar = "AWS_SECURITY_TOKEN"
sessionTokenEnvVar = "AWS_SESSION_TOKEN"
awsRegionEnvVar = "AWS_REGION"
awsRoleArnEnvVar = "AWS_ROLE_ARN"
awsWebIdentityTokenFileEnvVar = "AWS_WEB_IDENTITY_TOKEN_FILE"
awsCredentialsFileEnvVar = "AWS_SHARED_CREDENTIALS_FILE"
awsProfileEnvVar = "AWS_PROFILE"
// ref. https://docs.aws.amazon.com/sdkref/latest/guide/settings-global.html
accessKeyGlobalSetting = "aws_access_key_id"
secretKeyGlobalSetting = "aws_secret_access_key"
securityTokenGlobalSetting = "aws_session_token"
)
// awsCredentialService represents the interface for AWS credential providers
type awsCredentialService interface {
credentials() (providers.AWSCredentials, error)
}
// awsEnvironmentCredentialService represents an static environment-variable credential provider for AWS
type awsEnvironmentCredentialService struct {
logger logging.Logger
}
func (cs *awsEnvironmentCredentialService) credentials() (providers.AWSCredentials, error) {
var creds providers.AWSCredentials
creds.AccessKey = os.Getenv(accessKeyEnvVar)
if creds.AccessKey == "" {
return creds, errors.New("no " + accessKeyEnvVar + " set in environment")
}
creds.SecretKey = os.Getenv(secretKeyEnvVar)
if creds.SecretKey == "" {
return creds, errors.New("no " + secretKeyEnvVar + " set in environment")
}
creds.RegionName = os.Getenv(awsRegionEnvVar)
if creds.RegionName == "" {
return creds, errors.New("no " + awsRegionEnvVar + " set in environment")
}
// SessionToken is required if using temporary ENV credentials from assumed IAM role
// Missing SessionToken results with 403 s3 error.
creds.SessionToken = os.Getenv(sessionTokenEnvVar)
if creds.SessionToken == "" {
// In case of missing SessionToken try to get SecurityToken
// AWS switched to use SessionToken, but SecurityToken was left for backward compatibility
creds.SessionToken = os.Getenv(securityTokenEnvVar)
}
return creds, nil
}
// awsProfileCredentialService represents a credential provider for AWS that extracts credentials from the AWS
// credentials file
type awsProfileCredentialService struct {
// Path to the credentials file.
//
// If empty will look for "AWS_SHARED_CREDENTIALS_FILE" env variable. If the
// env value is empty will default to current user's home directory.
// Linux/OSX: "$HOME/.aws/credentials"
// Windows: "%USERPROFILE%\.aws\credentials"
Path string `json:"path,omitempty"`
// AWS Profile to extract credentials from the credentials file. If empty
// will default to environment variable "AWS_PROFILE" or "default" if
// environment variable is also not set.
Profile string `json:"profile,omitempty"`
RegionName string `json:"aws_region"`
logger logging.Logger
}
func (cs *awsProfileCredentialService) credentials() (providers.AWSCredentials, error) {
var creds providers.AWSCredentials
filename, err := cs.path()
if err != nil {
return creds, err
}
cfg, err := ini.Load(filename)
if err != nil {
return creds, fmt.Errorf("failed to read credentials file: %v", err)
}
profile, err := cfg.GetSection(cs.profile())
if err != nil {
return creds, fmt.Errorf("failed to get profile: %v", err)
}
creds.AccessKey = profile.Key(accessKeyGlobalSetting).String()
if creds.AccessKey == "" {
return creds, fmt.Errorf("profile \"%v\" in credentials file %v does not contain \"%v\"", cs.Profile, cs.Path, accessKeyGlobalSetting)
}
creds.SecretKey = profile.Key(secretKeyGlobalSetting).String()
if creds.SecretKey == "" {
return creds, fmt.Errorf("profile \"%v\" in credentials file %v does not contain \"%v\"", cs.Profile, cs.Path, secretKeyGlobalSetting)
}
creds.SessionToken = profile.Key(securityTokenGlobalSetting).String() //default to empty string
if cs.RegionName == "" {
if cs.RegionName = os.Getenv(awsRegionEnvVar); cs.RegionName == "" {
return creds, errors.New("no " + awsRegionEnvVar + " set in environment or configuration")
}
}
creds.RegionName = cs.RegionName
return creds, nil
}
func (cs *awsProfileCredentialService) path() (string, error) {
if len(cs.Path) != 0 {
return cs.Path, nil
}
if cs.Path = os.Getenv(awsCredentialsFileEnvVar); len(cs.Path) != 0 {
return cs.Path, nil
}
homeDir, err := os.UserHomeDir()
if err != nil {
return "", fmt.Errorf("user home directory not found: %w", err)
}
cs.Path = filepath.Join(homeDir, ".aws", "credentials")
return cs.Path, nil
}
func (cs *awsProfileCredentialService) profile() string {
if cs.Profile != "" {
return cs.Profile
}
cs.Profile = os.Getenv(awsProfileEnvVar)
if cs.Profile == "" {
cs.Profile = "default"
}
return cs.Profile
}
// awsMetadataCredentialService represents an EC2 metadata service credential provider for AWS
type awsMetadataCredentialService struct {
RoleName string `json:"iam_role,omitempty"`
RegionName string `json:"aws_region"`
creds providers.AWSCredentials
expiration time.Time
credServicePath string
tokenPath string
logger logging.Logger
}
func (cs *awsMetadataCredentialService) urlForMetadataService() (string, error) {
// override default path for testing
if cs.credServicePath != "" {
return cs.credServicePath + cs.RoleName, nil
}
// otherwise, normal flow
// if a role name is provided, look up via the EC2 credential service
if cs.RoleName != "" {
return ec2DefaultCredServicePath + cs.RoleName, nil
}
// otherwise, check environment to see if it looks like we're in an ECS
// container (with implied role association)
if isECS() {
return ecsDefaultCredServicePath + os.Getenv(ecsRelativePathEnvVar), nil
}
// if there's no role name and we don't appear to have a path to the
// ECS container service, then the configuration is invalid
return "", errors.New("metadata endpoint cannot be determined from settings and environment")
}
func (cs *awsMetadataCredentialService) tokenRequest() (*http.Request, error) {
tokenURL := ec2DefaultTokenPath
if cs.tokenPath != "" {
// override for testing
tokenURL = cs.tokenPath
}
req, err := http.NewRequest(http.MethodPut, tokenURL, nil)
if err != nil {
return nil, err
}
// we are going to use the token in the immediate future, so a long TTL is not necessary
req.Header.Set("X-aws-ec2-metadata-token-ttl-seconds", "60")
return req, nil
}
func (cs *awsMetadataCredentialService) refreshFromService() error {
// define the expected JSON payload from the EC2 credential service
// ref. https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/iam-roles-for-amazon-ec2.html
type metadataPayload struct {
Code string
AccessKeyID string `json:"AccessKeyId"`
SecretAccessKey string
Token string
Expiration time.Time
}
// short circuit if a reasonable amount of time until credential expiration remains
if time.Now().Add(time.Minute * 5).Before(cs.expiration) {
cs.logger.Debug("Credentials previously obtained from metadata service still valid.")
return nil
}
cs.logger.Debug("Obtaining credentials from metadata service.")
metaDataURL, err := cs.urlForMetadataService()
if err != nil {
// configuration issue or missing ECS environment
return err
}
// construct an HTTP client with a reasonably short timeout
client := &http.Client{Timeout: time.Second * 10}
req, err := http.NewRequest(http.MethodGet, metaDataURL, nil)
if err != nil {
return errors.New("unable to construct metadata HTTP request: " + err.Error())
}
// if in the EC2 environment, we will use IMDSv2, which requires a session cookie from a
// PUT request on the token endpoint before it will give the credentials, this provides
// protection from SSRF attacks
if !isECS() {
tokenReq, err := cs.tokenRequest()
if err != nil {
return errors.New("unable to construct metadata token HTTP request: " + err.Error())
}
body, err := doMetaDataRequestWithClient(tokenReq, client, "metadata token", cs.logger)
if err != nil {
return err
}
// token is the body of response; add to header of metadata request
req.Header.Set("X-aws-ec2-metadata-token", string(body))
}
body, err := doMetaDataRequestWithClient(req, client, "metadata", cs.logger)
if err != nil {
return err
}
var payload metadataPayload
err = json.Unmarshal(body, &payload)
if err != nil {
return errors.New("failed to parse credential response from metadata service: " + err.Error())
}
// Only the EC2 endpoint returns the "Code" element which indicates whether the query was
// successful; the ECS endpoint does not! Some other fields are missing in the ECS payload
// but we do not depend on them.
if cs.RoleName != "" && payload.Code != "Success" {
return errors.New("metadata service query did not succeed: " + payload.Code)
}
cs.expiration = payload.Expiration
cs.creds.AccessKey = payload.AccessKeyID
cs.creds.SecretKey = payload.SecretAccessKey
cs.creds.SessionToken = payload.Token
cs.creds.RegionName = cs.RegionName
return nil
}
func (cs *awsMetadataCredentialService) credentials() (providers.AWSCredentials, error) {
err := cs.refreshFromService()
if err != nil {
return cs.creds, err
}
return cs.creds, nil
}
// awsWebIdentityCredentialService represents an STS WebIdentity credential services
type awsWebIdentityCredentialService struct {
RoleArn string
WebIdentityTokenFile string
RegionName string `json:"aws_region"`
SessionName string `json:"session_name"`
stsURL string
creds providers.AWSCredentials
expiration time.Time
logger logging.Logger
}
func (cs *awsWebIdentityCredentialService) populateFromEnv() error {
cs.RoleArn = os.Getenv(awsRoleArnEnvVar)
if cs.RoleArn == "" {
return errors.New("no " + awsRoleArnEnvVar + " set in environment")
}
cs.WebIdentityTokenFile = os.Getenv(awsWebIdentityTokenFileEnvVar)
if cs.WebIdentityTokenFile == "" {
return errors.New("no " + awsWebIdentityTokenFileEnvVar + " set in environment")
}
if cs.RegionName == "" {
if cs.RegionName = os.Getenv(awsRegionEnvVar); cs.RegionName == "" {
return errors.New("no " + awsRegionEnvVar + " set in environment or configuration")
}
}
return nil
}
func (cs *awsWebIdentityCredentialService) stsPath() string {
var stsPath string
switch {
case cs.stsURL != "":
stsPath = cs.stsURL
case cs.RegionName != "":
stsPath = fmt.Sprintf(stsRegionPath, strings.ToLower(cs.RegionName))
default:
stsPath = stsDefaultPath
}
return stsPath
}
func (cs *awsWebIdentityCredentialService) refreshFromService() error {
// define the expected JSON payload from the EC2 credential service
// ref. https://docs.aws.amazon.com/STS/latest/APIReference/API_AssumeRoleWithWebIdentity.html
type responsePayload struct {
Result struct {
Credentials struct {
SessionToken string
SecretAccessKey string
Expiration time.Time
AccessKeyID string `xml:"AccessKeyId"`
}
} `xml:"AssumeRoleWithWebIdentityResult"`
}
// short circuit if a reasonable amount of time until credential expiration remains
if time.Now().Add(time.Minute * 5).Before(cs.expiration) {
cs.logger.Debug("Credentials previously obtained from sts service still valid.")
return nil
}
cs.logger.Debug("Obtaining credentials from sts for role %s.", cs.RoleArn)
var sessionName string
if cs.SessionName == "" {
sessionName = "open-policy-agent"
} else {
sessionName = cs.SessionName
}
tokenData, err := os.ReadFile(cs.WebIdentityTokenFile)
if err != nil {
return errors.New("unable to read web token for sts HTTP request: " + err.Error())
}
token := string(tokenData)
queryVals := url.Values{
"Action": []string{"AssumeRoleWithWebIdentity"},
"RoleSessionName": []string{sessionName},
"RoleArn": []string{cs.RoleArn},
"WebIdentityToken": []string{token},
"Version": []string{"2011-06-15"},
}
stsRequestURL, _ := url.Parse(cs.stsPath())
// construct an HTTP client with a reasonably short timeout
client := &http.Client{Timeout: time.Second * 10}
req, err := http.NewRequest(http.MethodPost, stsRequestURL.String(), strings.NewReader(queryVals.Encode()))
if err != nil {
return errors.New("unable to construct STS HTTP request: " + err.Error())
}
req.Header.Add("Content-Type", "application/x-www-form-urlencoded")
body, err := doMetaDataRequestWithClient(req, client, "STS", cs.logger)
if err != nil {
return err
}
var payload responsePayload
err = xml.Unmarshal(body, &payload)
if err != nil {
return errors.New("failed to parse credential response from STS service: " + err.Error())
}
cs.expiration = payload.Result.Credentials.Expiration
cs.creds.AccessKey = payload.Result.Credentials.AccessKeyID
cs.creds.SecretKey = payload.Result.Credentials.SecretAccessKey
cs.creds.SessionToken = payload.Result.Credentials.SessionToken
cs.creds.RegionName = cs.RegionName
return nil
}
func (cs *awsWebIdentityCredentialService) credentials() (providers.AWSCredentials, error) {
err := cs.refreshFromService()
if err != nil {
return cs.creds, err
}
return cs.creds, nil
}
func isECS() bool {
// the special relative path URI is set by the container agent in the ECS environment only
_, isECS := os.LookupEnv(ecsRelativePathEnvVar)
return isECS
}
func doMetaDataRequestWithClient(req *http.Request, client *http.Client, desc string, logger logging.Logger) ([]byte, error) {
// convenience function to get the body of an AWS EC2 metadata service request with
// appropriate error-handling boilerplate and logging for this special case
resp, err := client.Do(req)
if err != nil {
// some kind of catastrophe talking to the EC2 service
return nil, errors.New(desc + " HTTP request failed: " + err.Error())
}
defer resp.Body.Close()
logger.WithFields(map[string]interface{}{
"url": req.URL.String(),
"status": resp.Status,
"headers": resp.Header,
}).Debug("Received response from " + desc + " service.")
if resp.StatusCode != 200 {
if logger.GetLevel() == logging.Debug {
body, err := io.ReadAll(resp.Body)
if err != nil {
logger.Debug("Error response with response body: %v", body)
}
}
// could be 404 for role that's not available, but cover all the bases
return nil, errors.New(desc + " HTTP request returned unexpected status: " + resp.Status)
}
body, err := io.ReadAll(resp.Body)
if err != nil {
// deal with problems reading the body, whatever those might be
return nil, errors.New(desc + " HTTP response body could not be read: " + err.Error())
}
return body, nil
}
// signV4 modifies an http.Request to include an AWS V4 signature based on a credential provider
func signV4(req *http.Request, service string, credService awsCredentialService, theTime time.Time) error {
// General ref. https://docs.aws.amazon.com/general/latest/gr/sigv4_signing.html
// S3 ref. https://docs.aws.amazon.com/AmazonS3/latest/API/sigv4-auth-using-authorization-header.html
// APIGateway ref. https://docs.aws.amazon.com/apigateway/api-reference/signing-requests/
var body []byte
if req.Body == nil {
body = []byte("")
} else {
var err error
body, err = io.ReadAll(req.Body)
if err != nil {
return errors.New("error getting request body: " + err.Error())
}
// Since ReadAll consumed the body ReadCloser, we must create a new ReadCloser for the request so that the
// subsequent read starts from the beginning
req.Body = io.NopCloser(bytes.NewReader(body))
}
creds, err := credService.credentials()
if err != nil {
return errors.New("error getting AWS credentials: " + err.Error())
}
now := theTime.UTC()
authHeader, awsHeaders := providers.AWSSignV4(req.Header, req.Method, req.URL, body, service, creds, now)
req.Header.Set("Authorization", authHeader)
for k, v := range awsHeaders {
req.Header.Add(k, v)
}
return nil
}