[MBL-19721] Fix Studio video transcript download in Android

Intercept Instructure Media caption file downloads in CanvasWebView
by checking for Authorization header to distinguish actual user-initiated
downloads from resource loads during page initialization.

refs: MBL-19721
test-plan: NONE

Author: kristofnemere

libs/pandautils/src/main/java/com/instructure/pandautils/views/CanvasWebView.kt

@@ -226,6 +226,9 @@ class CanvasWebView @JvmOverloads constructor(
                 if (isInternalFileDownloadLink(url)) {
                     val fileName = parseFileNameFromContentDisposition(contentDisposition, url)
                     mediaDownloadCallback?.downloadInternalMedia(mimetype, url, fileName)
+                } else if (isInstructureMediaDrmDownload(url)) {
+                    val fileName = parseFileNameFromContentDisposition(contentDisposition, url)
+                    mediaDownloadCallback?.downloadInternalMedia(mimetype, url, fileName)
                 } else if (contentDisposition != null) {
                     val fileName = parseFileNameFromContentDisposition(contentDisposition, url)
                     canvasWebViewClientCallback?.openMediaFromWebView(mimetype, url, fileName)
@@ -425,6 +428,18 @@ class CanvasWebView @JvmOverloads constructor(
                 mediaDownloadCallback?.downloadMedia("", url, fileName)
                 view.post { stopLoading() } // Hack to stop loading the file in the WebView, since returning an empty response breaks what's being shown
             }
+
+            if (isInstructureMediaCaptionFile(url) &&
+                request.hasGesture() &&
+                request.requestHeaders.containsKey("Authorization") &&
+                mediaDownloadCallback != null
+            ) {
+                val fileName = parseFileNameFromContentDisposition(url, url)
+                mediaDownloadCallback?.downloadInternalMedia(null, url, fileName)
+                view.post { stopLoading() }
+                return WebResourceResponse(null, null, null)
+            }
+
             return super.shouldInterceptRequest(view, request)
         }
 
@@ -1006,6 +1021,14 @@ class CanvasWebView @JvmOverloads constructor(
             return url.contains("canvadocs") && url.contains("/download/") && url.contains("single_use_token=")
         }
 
+        private fun isInstructureMediaDrmDownload(url: String): Boolean {
+            return url.contains("instructuremedia.com") && url.contains("/downloadables/")
+        }
+
+        private fun isInstructureMediaCaptionFile(url: String): Boolean {
+            return url.contains("instructuremedia.com") && url.contains("/api/media_management/caption_files/")
+        }
+
         fun containsLTI(html: String, encoding: String?): Boolean {
             // BaseURL is set as Referer. Referer needed for some Vimeo videos to play
             // Studio needs the protocol attached to the referrer, so use that if we're using Studio