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Add DpopHeaderGenerator
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‎services/signin/pom.xml‎

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<artifactId>http-auth-aws</artifactId>
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<version>${awsjavasdk.version}</version>
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</dependency>
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<dependency>
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<groupId>software.amazon.awssdk</groupId>
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<artifactId>third-party-jackson-core</artifactId>
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<version>${awsjavasdk.version}</version>
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</dependency>
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</dependencies>
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</project>

‎services/signin/src/main/java/software/amazon/awssdk/services/signin/internal/DpopHeaderGenerator.java‎

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/*
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* Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
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*
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* Licensed under the Apache License, Version 2.0 (the "License").
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* You may not use this file except in compliance with the License.
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* A copy of the License is located at
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*
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* http://aws.amazon.com/apache2.0
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*
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* or in the "license" file accompanying this file. This file is distributed
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* on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
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* express or implied. See the License for the specific language governing
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* permissions and limitations under the License.
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*/
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package software.amazon.awssdk.services.signin.internal;
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import java.io.ByteArrayOutputStream;
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import java.io.IOException;
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import java.nio.charset.StandardCharsets;
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import java.security.Signature;
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import java.security.interfaces.ECPrivateKey;
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import java.security.interfaces.ECPublicKey;
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import java.security.spec.ECPoint;
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import java.util.Arrays;
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import java.util.Base64;
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import software.amazon.awssdk.annotations.SdkInternalApi;
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import software.amazon.awssdk.thirdparty.jackson.core.JsonFactory;
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import software.amazon.awssdk.thirdparty.jackson.core.JsonGenerator;
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import software.amazon.awssdk.utils.Pair;
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/**
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* Utilities that implement rfc9449 - OAuth 2.0 Demonstrating Proof of Possession (DPoP)
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*/
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@SdkInternalApi
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public final class DpopHeaderGenerator {
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public static final int ES256_SIGNATURE_BYTE_LENGTH = 64;
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public static final byte DER_SEQUENCE_TAG = 0x30;
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private DpopHeaderGenerator() {}
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/**
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* Construct a rfc9449 - OAuth 2.0 Demonstrating Proof of Possession (DPoP) header.
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*
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* The DPoP HTTP header must be a signed JWT (RFC 7519: JSON Web Token), which includes a
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* JWK (RFC 7517: JSON Web Key).
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*
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* For reference, see:
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* <ul>
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* <li><a href="https://datatracker.ietf.org/doc/html/rfc9449">RFC 9449 -
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* OAuth 2.0 Demonstrating Proof of Possession (DPoP)</a></li>
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* <li><a href="https://datatracker.ietf.org/doc/html/rfc7519">RFC 7519 - JSON Web Token (JWT)</a></li>
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* <li><a href="https://datatracker.ietf.org/doc/html/rfc7517">RFC 7517 - JSON Web Key (JWK)</a></li>
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* </ul>
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*
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* @param pemContent - EC1 / RFC 5915 ASN.1 formated PEM contents
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* @param endpoint - The HTTP target URI (Section 7.1 of [RFC9110]) of the request to which the JWT is attached,
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* without query and fragment parts
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* @param epochSeconds - creation time of the JWT in epoch seconds.
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* @param uuid - Unique identifier for the DPoP proof JWT - should be a UUID4 string.
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* @return DPoP header value
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* @throws Exception
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*/
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public static String generateDPoPProofHeader(String pemContent, String endpoint, long epochSeconds, String uuid)
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throws Exception {
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// Load EC public and private key from PEM
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Pair<ECPrivateKey, ECPublicKey> keys = EcKeyLoader.loadSec1Pem(pemContent);
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ECPrivateKey privateKey = keys.left();
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ECPublicKey publicKey = keys.right();
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// Build JSON strings (header, payload) with JsonGenerator
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String headerJson = buildHeaderJson(publicKey);
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String payloadJson = buildPayloadJson(uuid, endpoint, epochSeconds);
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// Base64URL encode header + payload
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String encodedHeader = base64UrlEncode(headerJson.getBytes(StandardCharsets.UTF_8));
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String encodedPayload = base64UrlEncode(payloadJson.getBytes(StandardCharsets.UTF_8));
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String message = encodedHeader + "." + encodedPayload;
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// Sign (ES256)
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Signature signature = Signature.getInstance("SHA256withECDSA");
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signature.initSign(privateKey);
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signature.update(message.getBytes(StandardCharsets.UTF_8));
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byte[] signatureBytes = translateDerSignatureToJws(signature.sign(), ES256_SIGNATURE_BYTE_LENGTH);
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// Combine into JWT
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String encodedSignature = base64UrlEncode(signatureBytes);
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return message + "." + encodedSignature;
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}
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// build the JWT header which includes the public key
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private static String buildHeaderJson(ECPublicKey publicKey) throws IOException {
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ECPoint pubPoint = publicKey.getW();
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String x = base64UrlEncode(stripLeadingZero(pubPoint.getAffineX().toByteArray()));
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String y = base64UrlEncode(stripLeadingZero(pubPoint.getAffineY().toByteArray()));
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ByteArrayOutputStream out = new ByteArrayOutputStream();
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JsonFactory factory = new JsonFactory();
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try (JsonGenerator gen = factory.createGenerator(out)) {
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gen.writeStartObject();
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gen.writeStringField("typ", "dpop+jwt");
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gen.writeStringField("alg", "ES256");
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gen.writeObjectFieldStart("jwk");
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gen.writeStringField("crv", "P-256");
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gen.writeStringField("kty", "EC");
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gen.writeStringField("x", x);
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gen.writeStringField("y", y);
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gen.writeEndObject(); // end jwk
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gen.writeEndObject(); // end root
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}
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return out.toString();
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}
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private static String buildPayloadJson(String uuid, String endpoint, long epochSeconds) throws IOException {
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ByteArrayOutputStream out = new ByteArrayOutputStream();
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JsonFactory factory = new JsonFactory();
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try (JsonGenerator gen = factory.createGenerator(out)) {
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gen.writeStartObject();
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gen.writeStringField("jti", uuid);
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gen.writeStringField("htm", "POST");
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gen.writeStringField("htu", endpoint);
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gen.writeNumberField("iat", epochSeconds);
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gen.writeEndObject();
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}
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return out.toString();
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}
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/**
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* Java Signature from SHA256withECDSA produces an ASN.1/DER encoded signature.
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* This method translates that signature into the concatenated (R,S) format expected by JWS.
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*
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* An ECDSA signature always produces two big integers: R and S. The DER format encodes these in a variable
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* length sequence because the values are encoded without leading zeroes with a structure following:
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* [ SEQUENCE_TAG, total_length, INTEGER_TAG, length of R, (bytes of R), INTEGER_TAG, length OF S, ( bytes of S) ]
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*
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* The JWT/JOSE spec defines ECDSA signatures as two 32 byte, big-endian integer values for R and S (total of 64 bytes):
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* [ 32 bytes of R, 32 bytes of S]
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*
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* @param derSignature The ASN1/DER-encoded signature.
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* @param outputLength The expected length of the ECDSA JWS signature. This should be 64 for ES256
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*
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* @return The ECDSA JWS encoded signature (concatenated r,s values)
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**/
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private static byte[] translateDerSignatureToJws(byte[] derSignature, int outputLength)
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throws Exception {
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// validate DER signature format
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if (derSignature.length < 8 || derSignature[0] != DER_SEQUENCE_TAG) {
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throw new RuntimeException("Invalid ECDSA signature format");
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}
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// the total length may be more than 1 byte
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// if the first byte is (0x81), its 2 bytes
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int offset; // point to the start of the first INTEGER_TAG
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if (derSignature[1] > 0) {
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offset = 2;
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} else if (derSignature[1] == (byte) 0x81) {
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offset = 3;
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} else {
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throw new RuntimeException("Invalid ECDSA signature format");
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}
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// get the length of R as the byte after the first INTEGER_TAG
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byte rLength = derSignature[offset + 1];
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// determine the number of significant (non-zero) bytes in R
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int i;
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int endOfR = offset + 2 + rLength;
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for (i = rLength; (i > 0) && (derSignature[endOfR - i] == 0); i--) {
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// do nothing
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}
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// get the length of S as the byte after the second INTEGER_TAG which is:
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byte sLength = derSignature[endOfR + 1];
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// determine number of significant bytes in S
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int j;
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int endOfS = endOfR + 2 + sLength;
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for (j = sLength; (j > 0) && (derSignature[endOfS - j] == 0); j--) {
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// do nothing
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}
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int rawLen = Math.max(i, j);
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rawLen = Math.max(rawLen, outputLength / 2);
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// sanity check, ensure the internal structure matches the DER spec.
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if ((derSignature[offset - 1] & 0xff) != derSignature.length - offset
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|| (derSignature[offset - 1] & 0xff) != 2 + rLength + 2 + sLength
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|| derSignature[offset] != 2
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|| derSignature[endOfR] != 2) {
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throw new RuntimeException("Invalid ECDSA signature format");
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}
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final byte[] jwsSignature = new byte[2 * rawLen];
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// copy the significant bytes of R (i bytes), removing any leading zeros, into the first half of output array.
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// Right aligned!
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System.arraycopy(derSignature, endOfR - i, jwsSignature, rawLen - i, i);
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// do the same for S to the second half of the output array. Also right aligned.
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System.arraycopy(derSignature, (offset + 2 + rLength + 2 + sLength) - j, jwsSignature, 2 * rawLen - j, j);
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return jwsSignature;
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}
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private static String base64UrlEncode(byte[] data) {
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return Base64.getUrlEncoder().withoutPadding().encodeToString(data);
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}
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private static byte[] stripLeadingZero(byte[] bytes) {
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if (bytes.length > 1 && bytes[0] == 0x00) {
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return Arrays.copyOfRange(bytes, 1, bytes.length);
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}
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return bytes;
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}
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public static void main(String[] args) throws Exception {
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String pem = "-----BEGIN EC PRIVATE KEY-----\n"
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+ "MHcCAQEEICeY73qhQO/3o1QnrL5Nu3HMDB9h3kVW6imRdcHks0tboAoGCCqGSM49"
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+ "AwEHoUQDQgAEbefyxjd/UlGwAPF6hy0k4yCW7dSghc6yPd4To0sBqX0tPS/aoLrl"
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+ "QnPjfDslgD29p4+Pgwxj1s8cFHVeDKdKTQ==\n"
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+ "-----END EC PRIVATE KEY-----";
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String dpopHeader = DpopHeaderGenerator.generateDPoPProofHeader(
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pem, "https://ap-northeast-1.aws-signin-testing.amazon.com/v1/token",
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1760727856,
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"c7cf0359-f736-4a55-bbc1-70f6a0e2d55d"
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);
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System.out.println("\n\nDPOP Proof header:\n" + dpopHeader);
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}
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}

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