BuildSession(ProjectBuildingRequest request, boolean localProjects) {
            this.request = request;
            this.session =
                    RepositoryUtils.overlay(request.getLocalRepository(), request.getRepositorySession(), repoSystem);
            InternalSession.from(session);
            this.repositories = RepositoryUtils.toRepos(request.getRemoteRepositories());

        ModelBuilderRequestBuilder(ModelBuilderRequest request) {
            this.session = request.getSession();
            this.validationLevel = request.getValidationLevel();
            this.locationTracking = request.isLocationTracking();
            this.twoPhaseBuilding = request.isTwoPhaseBuilding();
            this.source = request.getSource();
            this.projectBuild = request.isProjectBuild();

    }

    @Override
    public ModelBuilderResult build(ModelBuilderRequest request) throws ModelBuilderException {
        request = fillRequestDefaults(request);
        if (request.getInterimResult() != null) {
            return build(request, request.getInterimResult(), new LinkedHashSet<>());
        } else {
            return build(request, new LinkedHashSet<>());
        }
    }

    @Override
    public ArtifactResolverResult resolve(ArtifactResolverRequest request)
            throws ArtifactResolverException, IllegalArgumentException {
        nonNull(request, "request");
        InternalSession session = InternalSession.from(request.getSession());
        try {
            Map<Artifact, Path> paths = new HashMap<>();

        request.projectBuild(true);
        request.session(InternalSession.from(session));
        request.source(ModelSource.fromPath(src));
        request.validationLevel(ModelBuilderRequest.VALIDATION_LEVEL_MINIMAL);
        request.locationTracking(false);
        request.modelResolver(modelResolver);

You could create an API with a *path operation* that could trigger a request to an *external API* created by someone else (probably the same developer that would be *using* your API).

The process that happens when your API app calls the *external API* is named a "callback". Because the software that the external developer wrote sends a request to your API and then your API *calls back*, sending a request to an *external API* (that was probably created by the same developer).

	errFatal(err)

	// Start sending requests.
	go func() {
		for i := byte(0); i < 100; i++ {
			st.Requests <- []byte{i}
		}
		close(st.Requests)
	}()
	// Now do 100 other requests to ensure that the server doesn't block.
	for i := 0; i < 100; i++ {
		_, err := remoteConn.Request(ctx, handlerTest2, []byte(testPayload))
		errFatal(err)
	}
	// Start processing requests.
	close(processHandler)

    private Model loadPom(
            RepositorySystemSession session, ArtifactDescriptorRequest request, ArtifactDescriptorResult result)
            throws ArtifactDescriptorException {
        RequestTrace trace = RequestTrace.newChild(request.getTrace(), request);

        LinkedHashSet<String> visited = new LinkedHashSet<>();
        for (Artifact a = request.getArtifact(); ; ) {

	for _, ep := range testServer.Disks {
		for _, disk := range ep.Endpoints {
			os.RemoveAll(disk.Path)
		}
	}
}

// Truncate request to simulate unexpected EOF for a request signed using streaming signature v4.
func truncateChunkByHalfSigv4(req *http.Request) (*http.Request, error) {
	bufReader := bufio.NewReader(req.Body)
	hexChunkSize, chunkSignature, err := readChunkLine(bufReader)
	if err != nil {
		return nil, err

You also define in some way at which **moments** your app will send those requests or events.

And **your users** define in some way (for example in a web dashboard somewhere) the **URL** where your app should send those requests.