Issue with setting up basic auth header in SOAP request

I'm using Spring Boot and I'm trying to configure web service template to append basic authentication headers on every SOAP request.

Here is my configuration class:

@Configuration
public class SoapClientConfiguration {

    private static final Logger LOGGER = LoggerFactory.getLogger(SoapClientConfiguration.class);

    private final DmsConfiguration dmsConfiguration;

    public SoapClientConfiguration(DmsConfiguration dmsConfiguration) {
        this.dmsConfiguration = dmsConfiguration;
    }


    /**
     * Method for generating POJO objects from xml at pointed location
     *
     * @return Jaxb2Marshaller instance.
     */
    @Bean
    public Jaxb2Marshaller marshaller()
    {
        Jaxb2Marshaller marshaller = new Jaxb2Marshaller();
        marshaller.setPackagesToScan(dmsConfiguration.getJaxbPackageLocation());
        return marshaller;
    }

    /**
     * Configuring DMS web service client
     *
     * @param marshaller jaxb2 marshaller
     * @return DmsWebServiceClient Object
     */
    @Bean
    public DmsWebServiceClient dmsWebServiceClient(Jaxb2Marshaller marshaller)
        throws NoSuchAlgorithmException, KeyStoreException, KeyManagementException
    {
        DmsWebServiceClient dmsWebServiceClient = new DmsWebServiceClient();
        dmsWebServiceClient.setDefaultUri(
            dmsConfiguration.getProtocol() + "://" + dmsConfiguration.getConsumerServicesUri()
        );
        dmsWebServiceClient.setMarshaller(marshaller);
        dmsWebServiceClient.setUnmarshaller(marshaller);
        dmsWebServiceClient.setMessageSender(defaultMessageSender());

        return dmsWebServiceClient;
    }

    @Bean
    public HttpComponentsMessageSender defaultMessageSender()
        throws NoSuchAlgorithmException, KeyStoreException, KeyManagementException
    {
        return new HttpComponentsMessageSender(createHttpClient());
    }

    @Bean
    public HttpClient createHttpClient() throws NoSuchAlgorithmException, KeyStoreException, KeyManagementException
    {
        BasicHeader authHeader = new BasicHeader(
            "Authorization", "Basic " + dmsConfiguration.getBasicAuthenticationCredentials()
        );

        LOGGER.info("Web service credentials: {}", dmsConfiguration.getBasicAuthenticationCredentials());

        List<BasicHeader> authHeaders = Collections.singletonList(authHeader);
        RequestDefaultHeaders reqHeader = new RequestDefaultHeaders(authHeaders);

        return HttpClients.custom()
            .setSSLSocketFactory(sslConnectionSocketFactory())
            .addInterceptorFirst(new HttpComponentsMessageSender.RemoveSoapHeadersInterceptor())
            .addInterceptorLast(reqHeader)
            .setDefaultHeaders(authHeaders)
            .build();
    }

    public SSLConnectionSocketFactory sslConnectionSocketFactory()
        throws KeyStoreException, NoSuchAlgorithmException, KeyManagementException
    {
        return new SSLConnectionSocketFactory(sslContext(), NoopHostnameVerifier.INSTANCE);
    }

    public SSLContext sslContext() throws KeyStoreException, NoSuchAlgorithmException, KeyManagementException
    {
        TrustStrategy acceptingTrustStrategy = (X509Certificate[] chain, String authType) -> true;
        return SSLContexts.custom()
            .loadTrustMaterial(null, acceptingTrustStrategy)
            .build();
    }
}

and here is client configuration:

public class DmsWebServiceClient extends WebServiceGatewaySupport {

    private DmsCallbackConfiguration dmsCallbackConfiguration;

    /**
     * Getting or creating subject
     *
     * @param subject target subject
     * @return GetOrCreateSubjectResponse Object
     */
    public GetOrCreateSubjectResponse getOrCreateSubject(GetOrCreateSubjectRequest subject)
    {
        ObjectFactory objectFactory = new ObjectFactory();
        JAXBElement<GetOrCreateSubjectRequest> request = objectFactory.createGetOrCreateSubjectRequest(subject);

        return (GetOrCreateSubjectResponse) getWebServiceTemplate()
            .marshalSendAndReceive(request, new SoapActionCallback(dmsCallbackConfiguration.getCreateSubject()));
    }

    /**
     * Getting or creating document
     *
     * @param document target document
     * @return GetOrCreateDocumentResponse Object
     */
    public GetOrCreateDocumentResponse getOrCreateDocument(GetOrCreateDocumentRequest document)
    {
        ObjectFactory objectFactory = new ObjectFactory();
        JAXBElement<GetOrCreateDocumentRequest> request = objectFactory.createGetOrCreateDocumentRequest(document);

        return (GetOrCreateDocumentResponse) getWebServiceTemplate()
            .marshalSendAndReceive(request, new SoapActionCallback(dmsCallbackConfiguration.getCreateDocument()));
    }

    /**
     * Inserting attachment data
     *
     * @param attachment attachment input
     * @return InsertAttachmentResponse Object
     */
    public InsertAttachmentByDocumentIdResponse uploadAttachment(InsertAttachmentByDocumentIdRequest attachment)
    {
        ObjectFactory objectFactory = new ObjectFactory();
        JAXBElement<InsertAttachmentByDocumentIdRequest> request
            = objectFactory.createInsertAttachmentByDocumentIdRequest(attachment);

        return (InsertAttachmentByDocumentIdResponse) getWebServiceTemplate()
            .marshalSendAndReceive(request, new SoapActionCallback(dmsCallbackConfiguration.getInsertAttachment()));
    }

    @Autowired
    public void setDocumentSubjectConfiguration(DmsCallbackConfiguration dmsCallbackConfiguration) {
        this.dmsCallbackConfiguration = dmsCallbackConfiguration;
    }
}

Communication between services works fine but I'm getting 401 Unauthorized every time I send a request.

Do you have any idea what is wrong with my code?
Thank you in advance!

P.S. I have configure the logging and here is one example request:

<SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"><SOAP-ENV:Header/>
<SOAP-ENV:Body><ns2:GetOrCreateSubjectRequest xmlns:ns2="http://schemas.datacontract.org/2004/07/WCFService" xmlns:ns3="http://schemas.microsoft.com/2003/10/Serialization/Arrays"><ns2:Attributes><ns2:AttributeValue><ns2:IdAttribute>1084</ns2:IdAttribute><ns2:Value>test</ns2:Value></ns2:AttributeValue></ns2:Attributes><ns2:DefaultSettingsOverride>1</ns2:DefaultSettingsOverride><GetOrCreateSubjectRequest>7</GetOrCreateSubjectRequest><GetOrCreateSubjectRequest>1109953265147</GetOrCreateSubjectRequest><ns2:IdLanguage>2</ns2:IdLanguage><GetOrCreateSubjectRequest>1676</GetOrCreateSubjectRequest><ns2:IdUser>1304</ns2:IdUser><ns2:IdWorkflow>30</ns2:IdWorkflow><ns2:Name>Dosije klijenta</ns2:Name></ns2:GetOrCreateSubjectRequest></SOAP-ENV:Body></SOAP-ENV:Envelope>