How to extract public key from COSE message

[mhatrepratik11]

I have signed the CBOR message and stored COSE bytes in a file with below code.

private static void encodeMessageToCose(KeyPair keyPairWithKey1, KeyPair keyPairWithKey2) {
		try {
			ObjectMapper objectMapper = new ObjectMapper(new CBORFactory());
			TestVehicleManifestDto testVehicleManifestDto = TestVehicleManifestDto.getArtifactManifestDto();

			// Convert JSON to CBOR
			byte[] cborData = objectMapper.writeValueAsBytes(testVehicleManifestDto);

			OneKey oneKeyWithKey1 = new OneKey(keyPairWithKey1.getPublic(), keyPairWithKey1.getPrivate());
			Signer signerWithKey1 = new Signer(oneKeyWithKey1);
			signerWithKey1.addAttribute(HeaderKeys.Algorithm, AlgorithmID.ECDSA_256.AsCBOR(), COSE.Attribute.PROTECTED);
			signerWithKey1.addAttribute(HeaderKeys.KID, CBORObject.FromObject(KEY_1_ID), COSE.Attribute.PROTECTED);
			
			OneKey oneKeyWithKey2 = new OneKey(keyPairWithKey2.getPublic(), keyPairWithKey2.getPrivate());
			Signer signerWithKey2 = new Signer(oneKeyWithKey2);
			signerWithKey2.addAttribute(HeaderKeys.Algorithm, AlgorithmID.ECDSA_256.AsCBOR(), COSE.Attribute.PROTECTED);
			signerWithKey2.addAttribute(HeaderKeys.KID, CBORObject.FromObject(KEY_2_ID), COSE.Attribute.PROTECTED);

			// Create a Sign1Message
			SignMessage signMessage = new SignMessage();
			signMessage.addAttribute(HeaderKeys.CONTENT_TYPE, CBORObject.FromObject(VEHICLE_MANIFEST_MIME_TYPE_CONSTANT), COSE.Attribute.PROTECTED);
			signMessage.SetContent(cborData);
			signMessage.AddSigner(signerWithKey1);
			signMessage.AddSigner(signerWithKey2);
			signMessage.sign();

			byte[] coseBytes = signMessage.EncodeToBytes();
			System.out.println("COSE Byte data:  = " + Arrays.toString(coseBytes));

			// Write COSE bytes data to manifest file
			writeToManifestFile(coseBytes);

		} catch (CoseException | IOException e) {
			System.out.println("Error Occurred: " + e.getMessage());
		}
	}

Now, I want to get public key from this message. I have seen that signer does not expose any method to access OneKey directly. What is the other way by which I can achieve this?

Thanks in advance !