protected List<Path> parseExtClasspath(C context) throws Exception {
        ProtoSession protoSession = context.protoSession;
        String extClassPath = protoSession.getUserProperties().get(Constants.MAVEN_EXT_CLASS_PATH);
        if (extClassPath == null) {
            extClassPath = protoSession.getSystemProperties().get(Constants.MAVEN_EXT_CLASS_PATH);
            if (extClassPath != null) {

     * on his discretion, e.g. via the {@code -Dkey=value} parameter on the command line.
     *
     * @return The user properties, never {@code null}.
     */
    Properties getUserProperties();

    /**
     * Sets the user properties to use for interpolation. The user properties have been configured directly by the user

        } else {
            this.systemProperties = Collections.emptyMap();
        }

        return this;
    }

    @Override
    public Map<String, String> getUserProperties() {
        return userProperties;
    }

    /**
     * Sets the user properties to use for interpolation and profile activation. The user properties have been

            localRepositoryPath = request.getLocalRepositoryPath().getAbsolutePath();
        }

        if (localRepositoryPath == null || localRepositoryPath.isEmpty()) {
            String path = request.getUserProperties().getProperty(Constants.MAVEN_USER_CONF);
            if (path == null) {
                path = request.getSystemProperties().getProperty("user.home") + File.separator + ".m2";
            }

        Interpolator interpolator = new DefaultInterpolator();
        UnaryOperator<String> callback = v -> {
            String r = request.getUserProperties().getProperty(v);
            if (r == null) {
                r = request.getSystemProperties().getProperty(v);
            }
            return r != null ? r : v;
        };

            protoSession.getUserProperties().entrySet().stream()
                    .filter(k -> !sys.contains(k.getKey()))
                    .peek(k -> context.pushedUserProperties.add(k.getKey()))
                    .forEach(k -> System.setProperty(k.getKey(), k.getValue()));
        } else {
            protoSession.getUserProperties().entrySet().stream()

     * configured directly by the user on his discretion, e.g. via the {@code -Dkey=value} parameter on the command
     * line.
     *
     * @return The user properties, never {@code null}.
     */
    Properties getUserProperties();

    void setProject(MavenProject mavenProject);

    MavenProject getProject();

    ProjectBuildingRequest setProcessPlugins(boolean processPlugins);

    boolean isProcessPlugins();

        }
    }

    private UnaryOperator<String> createInterpolator(MavenExecutionRequest request) {
        UnaryOperator<String> callback = v -> {
            String r = request.getUserProperties().getProperty(v);
            if (r == null) {
                r = request.getSystemProperties().getProperty(v);
            }
            return r != null ? r : v;
        };

        String serializedSettings = writer.toString();

        RegexBasedInterpolator interpolator = new RegexBasedInterpolator();

        interpolator.addValueSource(new PropertiesBasedValueSource(request.getUserProperties()));

        interpolator.addValueSource(new PropertiesBasedValueSource(request.getSystemProperties()));

        try {
            interpolator.addValueSource(new EnvarBasedValueSource());

        //
        // Maven4: We may want to evaluate how this is used but we add these separate as the
        // getExecutionProperties is deprecated in MavenSession.
        //
        this.properties.putAll(session.getUserProperties());
        this.properties.putAll(session.getSystemProperties());

        String basedir = null;

        if (project != null) {
            File projectFile = project.getBasedir();