Fix SSLHandshake Exception by using bypass

CHANGELOG.md

@@ -21,6 +21,7 @@ Note that this project **does not** adhere to [Semantic Versioning](http://semve
 - We added two new fields to track the creation and most recent modification date and time for each entry. [koppor#130](https://github.com/koppor/jabref/issues/130)
 - We added a feature that allows the user to copy highlighted text in the preview window. [#6962](https://github.com/JabRef/jabref/issues/6962)
 - We added a feature that allows you to create new BibEntry via paste arxivId [#2292](https://github.com/JabRef/jabref/issues/2292)
+- We added a feature that allows the user to choose whether to trust the target site when unable to find a valid certification path from the file download site. [#7616](https://github.com/JabRef/jabref/issues/7616)
 
 ### Changed
 

src/main/java/org/jabref/gui/fieldeditors/LinkedFileViewModel.java

@@ -10,6 +10,9 @@
 import java.util.Optional;
 import java.util.function.BiPredicate;
 
+import javax.net.ssl.HostnameVerifier;
+import javax.net.ssl.HttpsURLConnection;
+import javax.net.ssl.SSLSocketFactory;
 import javax.xml.transform.TransformerException;
 
 import javafx.beans.Observable;
@@ -425,6 +428,10 @@ public void download() {
             }
 
             URLDownload urlDownload = new URLDownload(linkedFile.getLink());
+            if (!checkSSLHandshake(urlDownload)) {
+                return;
+            }
+
             BackgroundTask<Path> downloadTask = prepareDownloadTask(targetDirectory.get(), urlDownload);
             downloadTask.onSuccess(destination -> {
                 LinkedFile newLinkedFile = LinkedFilesEditorViewModel.fromFile(destination, databaseContext.getFileDirectories(filePreferences), externalFileTypes);
@@ -463,7 +470,28 @@ public void download() {
         }
     }
 
+    public boolean checkSSLHandshake(URLDownload urlDownload) {
+        try {
+            urlDownload.canBeReached();
+        } catch (kong.unirest.UnirestException ex) {
+            if (ex.getCause() instanceof javax.net.ssl.SSLHandshakeException) {
+                if (dialogService.showConfirmationDialogAndWait(Localization.lang("Download file"),
+                        Localization.lang("Unable to find valid certification path to requested target(%0), download anyway?",
+                                urlDownload.getSource().toString()))) {
+                    URLDownload.bypassSSLVerification();
+                    return true;
+                } else {
+                    dialogService.notify(Localization.lang("Download operation canceled."));
+                }
+            }
+            return false;
+        }
+        return true;
+    }
+
     public BackgroundTask<Path> prepareDownloadTask(Path targetDirectory, URLDownload urlDownload) {
+        SSLSocketFactory defaultSSLSocketFactory = HttpsURLConnection.getDefaultSSLSocketFactory();
+        HostnameVerifier defaultHostnameVerifier = HttpsURLConnection.getDefaultHostnameVerifier();
         BackgroundTask<Path> downloadTask = BackgroundTask
                 .wrap(() -> {
                     Optional<ExternalFileType> suggestedType = inferFileType(urlDownload);
@@ -476,6 +504,7 @@ public BackgroundTask<Path> prepareDownloadTask(Path targetDirectory, URLDownloa
                     return targetDirectory.resolve(fulltextDir).resolve(suggestedName);
                 })
                 .then(destination -> new FileDownloadTask(urlDownload.getSource(), destination))
+                .onFinished(() -> URLDownload.setSSLVerification(defaultSSLSocketFactory, defaultHostnameVerifier))
                 .onFailure(exception -> dialogService.showErrorDialogAndWait("Download failed", exception));
         return downloadTask;
     }

src/main/java/org/jabref/logic/net/URLDownload.java

@@ -36,6 +36,7 @@
 import javax.net.ssl.HostnameVerifier;
 import javax.net.ssl.HttpsURLConnection;
 import javax.net.ssl.SSLContext;
+import javax.net.ssl.SSLSocketFactory;
 import javax.net.ssl.TrustManager;
 import javax.net.ssl.X509TrustManager;
 
@@ -132,6 +133,20 @@ public X509Certificate[] getAcceptedIssuers() {
         }
     }
 
+    /**
+     *
+     * @param sf trust manager
+     * @param v host verifier
+     */
+    public static void setSSLVerification(SSLSocketFactory sf, HostnameVerifier v) {
+        try {
+            HttpsURLConnection.setDefaultSSLSocketFactory(sf);
+            HttpsURLConnection.setDefaultHostnameVerifier(v);
+        } catch (Exception e) {
+            LOGGER.error("A problem occurred when reset SSL verification", e);
+        }
+    }
+
     public URL getSource() {
         return source;
     }

src/main/resources/l10n/JabRef_en.properties

@@ -2292,3 +2292,6 @@ Import\ settings=Import settings
 Custom\ DOI\ URI=Custom DOI URI
 Customization=Customization
 Use\ custom\ DOI\ base\ URI\ for\ article\ access=Use custom DOI base URI for article access
+
+Unable\ to\ find\ valid\ certification\ path\ to\ requested\ target(%0),\ download\ anyway?=Unable to find valid certification path to requested target(%0), download anyway?
+Download\ operation\ canceled.=Download operation canceled.