AEM Cloud Service - No Authentication Presigned URL link for Author asset download

Adobe Experience Manager 2024.7.17964.20240726T172406Z-240700

Create a Blob Store PreSigned Url link for downloading assets from Author instance. Assuming file names are unique in repository, servlet searches for the given file name, gets full path and generates it. The link (when shared with users with no AEM Author access) does not ask for authentication and downloads the binary anonymously....

Check Oak Documentation for more details on direct binary access... 

Demo | Github

Link Generation : https://author-p10961-e1322140.adobeaemcloud.com/room-green.jpg.eaemPresigned

Add the Presigned url generation in a servlet apps.experienceaem.sites.core.servlets.AssetPresignedURL ..

package apps.experienceaem.sites.core.servlets;

import com.adobe.xfa.ut.StringUtils;
import com.day.cq.dam.api.Asset;
import com.day.cq.search.PredicateGroup;
import com.day.cq.search.Query;
import com.day.cq.search.QueryBuilder;
import com.day.cq.search.result.Hit;
import com.day.cq.search.result.SearchResult;
import org.apache.jackrabbit.api.binary.BinaryDownload;
import org.apache.jackrabbit.api.binary.BinaryDownloadOptions;
import org.apache.sling.api.SlingHttpServletRequest;
import org.apache.sling.api.SlingHttpServletResponse;
import org.apache.sling.api.resource.ResourceResolver;
import org.apache.sling.api.servlets.HttpConstants;
import org.apache.sling.api.servlets.SlingSafeMethodsServlet;
import org.osgi.framework.Constants;
import org.osgi.service.component.annotations.Component;
import org.osgi.service.component.annotations.Reference;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.jcr.Binary;
import javax.jcr.Session;
import javax.servlet.Servlet;
import javax.servlet.ServletException;
import java.net.URI;
import java.util.HashMap;
import java.util.Map;

@Component(
    immediate = true,
    service = Servlet.class,
    property = {
        Constants.SERVICE_DESCRIPTION + "=Experience AEM Presigned Download Urls",
        "sling.servlet.methods=" + HttpConstants.METHOD_GET,
        "sling.servlet.resourceTypes=sling/servlet/default",
        "sling.servlet.extensions=" + "eaemPresigned"
    }
)
public class AssetPresignedURLForDownload extends SlingSafeMethodsServlet {
    private final Logger logger = LoggerFactory.getLogger(getClass());

    @Reference
    private QueryBuilder builder;

    @Override
    protected void doGet(final SlingHttpServletRequest req, final SlingHttpServletResponse resp) {
        try{
            String fileName = req.getRequestPathInfo().getResourcePath();

            if(StringUtils.isEmpty(fileName)){
                throw new ServletException("Empty file name");
            }

            fileName = fileName.substring(1, fileName.lastIndexOf("."));

            ResourceResolver resolver = req.getResourceResolver();

            Query query = builder.createQuery(PredicateGroup.create(getPredicateMap(fileName)), resolver.adaptTo(Session.class));

            SearchResult result = query.getResult();
            String resourcePath = null;

            for (Hit hit : result.getHits()) {
                resourcePath = hit.getPath();
            }

            if(resourcePath == null){
                throw new ServletException("Resource not found with name : " + fileName);
            }

            Asset asset = resolver.getResource(resourcePath).adaptTo(Asset.class);
            Binary binary = asset.getOriginal().getBinary();

            if (!(binary instanceof BinaryDownload)) {
                resp.getWriter().println("Asset not of type BinaryDownload, download uri not available");
                return;
            }

            BinaryDownload binaryDownload = (BinaryDownload) binary;
            BinaryDownloadOptions downloadOptions = BinaryDownloadOptions.builder()
                .withMediaType(asset.getMimeType())
                .withFileName(asset.getName())
                .withDispositionTypeAttachment()
                .build();

            URI uri = binaryDownload.getURI(downloadOptions);

            resp.setContentType("text/html");
            resp.getWriter().println("No Authentication Required to Download the Asset, link below : <BR> <BR>" + uri.toString());
        } catch (Exception e) {
            logger.error("Error generating presigned link : ", e);
        }
    }

    private static Map<String, String> getPredicateMap(String fileName) {
        Map<String, String> map = new HashMap<>();

        map.put("type", "dam:Asset");
        map.put("nodename", fileName);
        map.put("p.limit", "1");

        return map;
    }
}