/
AwsCredentials.java
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/
AwsCredentials.java
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/*
* Copyright 2021 Google LLC
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following disclaimer
* in the documentation and/or other materials provided with the
* distribution.
*
* * Neither the name of Google LLC nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package com.google.auth.oauth2;
import com.google.api.client.http.GenericUrl;
import com.google.api.client.http.HttpContent;
import com.google.api.client.http.HttpHeaders;
import com.google.api.client.http.HttpMethods;
import com.google.api.client.http.HttpRequest;
import com.google.api.client.http.HttpRequestFactory;
import com.google.api.client.http.HttpResponse;
import com.google.api.client.json.GenericJson;
import com.google.api.client.json.JsonParser;
import com.google.common.annotations.VisibleForTesting;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLEncoder;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import javax.annotation.Nullable;
/**
* AWS credentials representing a third-party identity for calling Google APIs.
*
* <p>By default, attempts to exchange the external credential for a GCP access token.
*/
public class AwsCredentials extends ExternalAccountCredentials {
static final String AWS_IMDSV2_SESSION_TOKEN_HEADER = "x-aws-ec2-metadata-token";
static final String AWS_IMDSV2_SESSION_TOKEN_TTL_HEADER = "x-aws-ec2-metadata-token-ttl-seconds";
static final String AWS_IMDSV2_SESSION_TOKEN_TTL = "300";
/**
* The AWS credential source. Stores data required to retrieve the AWS credential from the AWS
* metadata server.
*/
static class AwsCredentialSource extends CredentialSource {
private static final String IMDSV2_SESSION_TOKEN_URL_FIELD_NAME = "imdsv2_session_token_url";
private final String regionUrl;
private final String url;
private final String regionalCredentialVerificationUrl;
private final String imdsv2SessionTokenUrl;
/**
* The source of the AWS credential. The credential source map must contain the
* `regional_cred_verification_url` field.
*
* <p>The `regional_cred_verification_url` is the regional GetCallerIdentity action URL, used to
* determine the account ID and its roles.
*
* <p>The `environment_id` is the environment identifier, in the format “aws${version}”. This
* indicates whether breaking changes were introduced to the underlying AWS implementation.
*
* <p>The `region_url` identifies the targeted region. Optional.
*
* <p>The `url` locates the metadata server used to retrieve the AWS credentials. Optional.
*/
AwsCredentialSource(Map<String, Object> credentialSourceMap) {
super(credentialSourceMap);
if (!credentialSourceMap.containsKey("regional_cred_verification_url")) {
throw new IllegalArgumentException(
"A regional_cred_verification_url representing the"
+ " GetCallerIdentity action URL must be specified.");
}
String environmentId = (String) credentialSourceMap.get("environment_id");
// Environment version is prefixed by "aws". e.g. "aws1".
Matcher matcher = Pattern.compile("(aws)([\\d]+)").matcher(environmentId);
if (!matcher.matches()) {
throw new IllegalArgumentException("Invalid AWS environment ID.");
}
int environmentVersion = Integer.parseInt(matcher.group(2));
if (environmentVersion != 1) {
throw new IllegalArgumentException(
String.format(
"AWS version %s is not supported in the current build.", environmentVersion));
}
this.regionUrl = (String) credentialSourceMap.get("region_url");
this.url = (String) credentialSourceMap.get("url");
this.regionalCredentialVerificationUrl =
(String) credentialSourceMap.get("regional_cred_verification_url");
if (credentialSourceMap.containsKey(IMDSV2_SESSION_TOKEN_URL_FIELD_NAME)) {
this.imdsv2SessionTokenUrl =
(String) credentialSourceMap.get(IMDSV2_SESSION_TOKEN_URL_FIELD_NAME);
} else {
this.imdsv2SessionTokenUrl = null;
}
this.validateMetadataServerUrls();
}
private void validateMetadataServerUrls() {
validateMetadataServerUrlIfAny(this.regionUrl, "region_url");
validateMetadataServerUrlIfAny(this.url, "url");
validateMetadataServerUrlIfAny(this.imdsv2SessionTokenUrl, "imdsv2_session_token_url");
}
@VisibleForTesting
static void validateMetadataServerUrlIfAny(String urlString, String nameInConfig) {
if (urlString == null || urlString.trim().length() == 0) {
return;
}
try {
URL url = new URL(urlString);
String host = url.getHost();
if (!host.equals("169.254.169.254") && !host.equals("[fd00:ec2::254]")) {
throw new IllegalArgumentException(
String.format("Invalid host %s for %s.", host, nameInConfig));
}
} catch (MalformedURLException malformedURLException) {
throw new IllegalArgumentException(malformedURLException);
}
}
}
private final AwsCredentialSource awsCredentialSource;
/** Internal constructor. See {@link AwsCredentials.Builder}. */
AwsCredentials(Builder builder) {
super(builder);
this.awsCredentialSource = (AwsCredentialSource) builder.credentialSource;
}
@Override
public AccessToken refreshAccessToken() throws IOException {
StsTokenExchangeRequest.Builder stsTokenExchangeRequest =
StsTokenExchangeRequest.newBuilder(retrieveSubjectToken(), getSubjectTokenType())
.setAudience(getAudience());
// Add scopes, if possible.
Collection<String> scopes = getScopes();
if (scopes != null && !scopes.isEmpty()) {
stsTokenExchangeRequest.setScopes(new ArrayList<>(scopes));
}
return exchangeExternalCredentialForAccessToken(stsTokenExchangeRequest.build());
}
@Override
public String retrieveSubjectToken() throws IOException {
Map<String, Object> metadataRequestHeaders = createMetadataRequestHeaders(awsCredentialSource);
// The targeted region is required to generate the signed request. The regional
// endpoint must also be used.
String region = getAwsRegion(metadataRequestHeaders);
AwsSecurityCredentials credentials = getAwsSecurityCredentials(metadataRequestHeaders);
// Generate the signed request to the AWS STS GetCallerIdentity API.
Map<String, String> headers = new HashMap<>();
headers.put("x-goog-cloud-target-resource", getAudience());
AwsRequestSigner signer =
AwsRequestSigner.newBuilder(
credentials,
"POST",
awsCredentialSource.regionalCredentialVerificationUrl.replace("{region}", region),
region)
.setAdditionalHeaders(headers)
.build();
AwsRequestSignature awsRequestSignature = signer.sign();
return buildSubjectToken(awsRequestSignature);
}
/** Clones the AwsCredentials with the specified scopes. */
@Override
public GoogleCredentials createScoped(Collection<String> newScopes) {
return new AwsCredentials((AwsCredentials.Builder) newBuilder(this).setScopes(newScopes));
}
private String retrieveResource(String url, String resourceName, Map<String, Object> headers)
throws IOException {
return retrieveResource(url, resourceName, HttpMethods.GET, headers, /* content= */ null);
}
private String retrieveResource(
String url,
String resourceName,
String requestMethod,
Map<String, Object> headers,
@Nullable HttpContent content)
throws IOException {
try {
HttpRequestFactory requestFactory = transportFactory.create().createRequestFactory();
HttpRequest request =
requestFactory.buildRequest(requestMethod, new GenericUrl(url), content);
HttpHeaders requestHeaders = request.getHeaders();
for (Map.Entry<String, Object> header : headers.entrySet()) {
requestHeaders.set(header.getKey(), header.getValue());
}
HttpResponse response = request.execute();
return response.parseAsString();
} catch (IOException e) {
throw new IOException(String.format("Failed to retrieve AWS %s.", resourceName), e);
}
}
private String buildSubjectToken(AwsRequestSignature signature)
throws UnsupportedEncodingException {
Map<String, String> canonicalHeaders = signature.getCanonicalHeaders();
List<GenericJson> headerList = new ArrayList<>();
for (String headerName : canonicalHeaders.keySet()) {
headerList.add(formatTokenHeaderForSts(headerName, canonicalHeaders.get(headerName)));
}
headerList.add(formatTokenHeaderForSts("Authorization", signature.getAuthorizationHeader()));
// The canonical resource name of the workload identity pool provider.
headerList.add(formatTokenHeaderForSts("x-goog-cloud-target-resource", getAudience()));
GenericJson token = new GenericJson();
token.setFactory(OAuth2Utils.JSON_FACTORY);
token.put("headers", headerList);
token.put("method", signature.getHttpMethod());
token.put(
"url",
awsCredentialSource.regionalCredentialVerificationUrl.replace(
"{region}", signature.getRegion()));
return URLEncoder.encode(token.toString(), "UTF-8");
}
Map<String, Object> createMetadataRequestHeaders(AwsCredentialSource awsCredentialSource)
throws IOException {
Map<String, Object> metadataRequestHeaders = new HashMap<>();
// AWS IDMSv2 introduced a requirement for a session token to be present
// with the requests made to metadata endpoints. This requirement is to help
// prevent SSRF attacks.
// Presence of "imdsv2_session_token_url" in Credential Source of config file
// will trigger a flow with session token, else there will not be a session
// token with the metadata requests.
// Both flows work for IDMS v1 and v2. But if IDMSv2 is enabled, then if
// session token is not present, Unauthorized exception will be thrown.
if (awsCredentialSource.imdsv2SessionTokenUrl != null) {
Map<String, Object> tokenRequestHeaders =
new HashMap<String, Object>() {
{
put(AWS_IMDSV2_SESSION_TOKEN_TTL_HEADER, AWS_IMDSV2_SESSION_TOKEN_TTL);
}
};
String imdsv2SessionToken =
retrieveResource(
awsCredentialSource.imdsv2SessionTokenUrl,
"Session Token",
HttpMethods.PUT,
tokenRequestHeaders,
/* content= */ null);
metadataRequestHeaders.put(AWS_IMDSV2_SESSION_TOKEN_HEADER, imdsv2SessionToken);
}
return metadataRequestHeaders;
}
@VisibleForTesting
String getAwsRegion(Map<String, Object> metadataRequestHeaders) throws IOException {
// For AWS Lambda, the region is retrieved through the AWS_REGION environment variable.
String region = getEnvironmentProvider().getEnv("AWS_REGION");
if (region != null) {
return region;
}
String defaultRegion = getEnvironmentProvider().getEnv("AWS_DEFAULT_REGION");
if (defaultRegion != null) {
return defaultRegion;
}
if (awsCredentialSource.regionUrl == null || awsCredentialSource.regionUrl.isEmpty()) {
throw new IOException(
"Unable to determine the AWS region. The credential source does not contain the region URL.");
}
region = retrieveResource(awsCredentialSource.regionUrl, "region", metadataRequestHeaders);
// There is an extra appended character that must be removed. If `us-east-1b` is returned,
// we want `us-east-1`.
return region.substring(0, region.length() - 1);
}
@VisibleForTesting
AwsSecurityCredentials getAwsSecurityCredentials(Map<String, Object> metadataRequestHeaders)
throws IOException {
// Check environment variables for credentials first.
String accessKeyId = getEnvironmentProvider().getEnv("AWS_ACCESS_KEY_ID");
String secretAccessKey = getEnvironmentProvider().getEnv("AWS_SECRET_ACCESS_KEY");
String token = getEnvironmentProvider().getEnv("AWS_SESSION_TOKEN");
if (accessKeyId != null && secretAccessKey != null) {
return new AwsSecurityCredentials(accessKeyId, secretAccessKey, token);
}
// Credentials not retrievable from environment variables - call metadata server.
// Retrieve the IAM role that is attached to the VM. This is required to retrieve the AWS
// security credentials.
if (awsCredentialSource.url == null || awsCredentialSource.url.isEmpty()) {
throw new IOException(
"Unable to determine the AWS IAM role name. The credential source does not contain the"
+ " url field.");
}
String roleName = retrieveResource(awsCredentialSource.url, "IAM role", metadataRequestHeaders);
// Retrieve the AWS security credentials by calling the endpoint specified by the credential
// source.
String awsCredentials =
retrieveResource(
awsCredentialSource.url + "/" + roleName, "credentials", metadataRequestHeaders);
JsonParser parser = OAuth2Utils.JSON_FACTORY.createJsonParser(awsCredentials);
GenericJson genericJson = parser.parseAndClose(GenericJson.class);
accessKeyId = (String) genericJson.get("AccessKeyId");
secretAccessKey = (String) genericJson.get("SecretAccessKey");
token = (String) genericJson.get("Token");
// These credentials last for a few hours - we may consider caching these in the
// future.
return new AwsSecurityCredentials(accessKeyId, secretAccessKey, token);
}
@VisibleForTesting
String getEnv(String name) {
return System.getenv(name);
}
private static GenericJson formatTokenHeaderForSts(String key, String value) {
// The GCP STS endpoint expects the headers to be formatted as:
// [
// {key: 'x-amz-date', value: '...'},
// {key: 'Authorization', value: '...'},
// ...
// ]
GenericJson header = new GenericJson();
header.setFactory(OAuth2Utils.JSON_FACTORY);
header.put("key", key);
header.put("value", value);
return header;
}
public static AwsCredentials.Builder newBuilder() {
return new AwsCredentials.Builder();
}
public static AwsCredentials.Builder newBuilder(AwsCredentials awsCredentials) {
return new AwsCredentials.Builder(awsCredentials);
}
public static class Builder extends ExternalAccountCredentials.Builder {
Builder() {}
Builder(AwsCredentials credentials) {
super(credentials);
}
@Override
public AwsCredentials build() {
return new AwsCredentials(this);
}
}
}