diff --git a/package.json b/package.json
index 8c80289..a20adf6 100644
--- a/package.json
+++ b/package.json
@@ -14,6 +14,7 @@
   },
   "homepage": "https://github.com/Xmader/musescore-downloader#readme",
   "dependencies": {
+    "md5": "^2.3.0",
     "pdfkit": "git+https://github.com/Xmader/pdfkit.git",
     "svg-to-pdfkit": "^0.1.8",
     "webmscore": "^0.10.4"
@@ -21,6 +22,7 @@
   "devDependencies": {
     "@rollup/plugin-json": "^4.0.0",
     "@types/file-saver": "^2.0.1",
+    "@types/md5": "^2.2.0",
     "@types/pdfkit": "^0.10.4",
     "rollup": "^1.26.3",
     "rollup-plugin-commonjs": "^10.1.0",
diff --git a/src/btn.ts b/src/btn.ts
index 5b82ff7..1b42c0c 100644
--- a/src/btn.ts
+++ b/src/btn.ts
@@ -1,5 +1,6 @@
 
 import { loadMscore, WebMscore } from './mscore'
+import { saveAs } from './utils'
 
 type BtnElement = HTMLButtonElement
 
@@ -86,8 +87,27 @@ export namespace BtnAction {
   export const PROCESSING_TEXT = 'Processing…'
   export const ERROR_TEXT = '❌Download Failed!'
 
-  export const openUrl = (url: string): BtnAction => {
-    return (): any => window.open(url)
+  type Promisable<T> = T | Promise<T>
+  type UrlInput = Promisable<string> | (() => Promisable<string>)
+
+  const normalizeUrlInput = (url: UrlInput) => {
+    if (typeof url === 'function') return url()
+    else return url
+  }
+
+  export const openUrl = (url: UrlInput): BtnAction => {
+    return process(async (): Promise<any> => {
+      window.open(await normalizeUrlInput(url))
+    })
+  }
+
+  export const download = (url: UrlInput, filename?: string): BtnAction => {
+    return process(async (): Promise<any> => {
+      const _url = await normalizeUrlInput(url)
+      const r = await fetch(_url)
+      const blob = await r.blob()
+      saveAs(blob, filename)
+    })
   }
 
   export const mscoreWindow = (fn: (w: Window, score: WebMscore, processingTextEl: ChildNode) => any): BtnAction => {
diff --git a/src/file.ts b/src/file.ts
new file mode 100644
index 0000000..355d36a
--- /dev/null
+++ b/src/file.ts
@@ -0,0 +1,32 @@
+
+import scoreinfo from './scoreinfo'
+import md5 from 'md5'
+
+const MAGIC = String(4 * 11 * 1607 * 2767) // '195649036' // I don't know what this is
+const AUTH_LEN = 4
+
+type FileType = 'img' | 'mp3' | 'midi'
+
+const getApiUrl = (type: FileType, index: number): string => {
+  // proxy
+  return `https://musescore.now.sh/api/jmuse?id=${scoreinfo.id}&type=${type}&index=${index}`
+}
+
+const getApiAuth = (type: FileType, index: number): string => {
+  const str = String(scoreinfo.id) + type + String(index) + MAGIC
+  return md5(str).slice(0, AUTH_LEN)
+}
+
+export const getFileUrl = async (type: FileType, index = 0): Promise<string> => {
+  const url = getApiUrl(type, index)
+  const auth = getApiAuth(type, index)
+
+  const r = await fetch(url, {
+    headers: {
+      Authorization: auth,
+    },
+  })
+
+  const { info } = await r.json()
+  return info.url as string
+}
diff --git a/src/main.ts b/src/main.ts
index 8919125..af3676b 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -3,6 +3,7 @@ import './meta'
 import { waitForDocumentLoaded, saveAs } from './utils'
 import { downloadPDF } from './pdf'
 import { downloadMscz } from './mscz'
+import { getFileUrl } from './file'
 import { getDownloadBtn, BtnList, BtnAction } from './btn'
 import * as recaptcha from './recaptcha'
 import scoreinfo from './scoreinfo'
@@ -16,6 +17,7 @@ const main = (): void => {
   recaptcha.init()
 
   const btnList = new BtnList(getDownloadBtn())
+  const filename = scoreinfo.fileName
 
   btnList.add({
     name: 'Download MSCZ',
@@ -32,19 +34,19 @@ const main = (): void => {
     action: BtnAction.mscoreWindow(async (w, score) => {
       const mxl = await score.saveMxl()
       const data = new Blob([mxl])
-      saveAs(data, `${scoreinfo.fileName}.mxl`)
+      saveAs(data, `${filename}.mxl`)
       w.close()
     }),
   })
 
   btnList.add({
     name: 'Download MIDI',
-    action: BtnAction.openUrl(scoreinfo.midiUrl),
+    action: BtnAction.download(() => getFileUrl('midi'), `${filename}.mid`),
   })
 
   btnList.add({
     name: 'Download MP3',
-    action: BtnAction.openUrl(scoreinfo.mp3Url),
+    action: BtnAction.download(() => getFileUrl('mp3'), `${filename}.mp3`),
   })
 
   btnList.add({
@@ -95,7 +97,6 @@ const main = (): void => {
 
         await score.setExcerptId(+id)
 
-        const filename = scoreinfo.fileName
         const data = new Blob([await score.savePdf()])
         saveAs(data, `${filename} - ${partName}.pdf`)
       }
diff --git a/src/pdf.ts b/src/pdf.ts
index c739ceb..0ff0984 100644
--- a/src/pdf.ts
+++ b/src/pdf.ts
@@ -1,5 +1,6 @@
 
 import { PDFWorkerHelper } from './worker-helper'
+import { getFileUrl } from './file'
 import { saveAs } from './utils'
 import scoreinfo from './scoreinfo'
 
@@ -26,9 +27,14 @@ export const downloadPDF = async (): Promise<void> => {
   const imgType = scoreinfo.sheetImgType
   const pageCount = scoreinfo.pageCount
 
-  const sheetImgURLs = Array.from({ length: pageCount }).map((_, i) => {
-    return scoreinfo.baseUrl + `score_${i}.${imgType}`
+  const rs = Array.from({ length: pageCount }).map((_, i) => {
+    if (i === 0) { // The url to the first page is static. We don't need to use API to obtain it.
+      return scoreinfo.baseUrl + `score_${i}.${imgType}`
+    } else { // obtain image urls using the API
+      return getFileUrl('img', i)
+    }
   })
+  const sheetImgURLs = await Promise.all(rs)
 
   return _downloadPDF(sheetImgURLs, imgType, scoreinfo.fileName)
 }
diff --git a/src/scoreinfo.ts b/src/scoreinfo.ts
index 143dd57..bbf97d9 100644
--- a/src/scoreinfo.ts
+++ b/src/scoreinfo.ts
@@ -38,14 +38,6 @@ const scoreinfo = {
     return origin + pathname.split('/').slice(0, -1).join('/') + '/'
   },
 
-  get midiUrl (this: typeof scoreinfo): string {
-    return this.baseUrl + 'score.mid'
-  },
-
-  get mp3Url (this: typeof scoreinfo): string {
-    return this.baseUrl + 'score.mp3'
-  },
-
   get msczUrl (this: typeof scoreinfo): string {
     // https://github.com/Xmader/cloudflare-worker-musescore-mscz
     return `https://musescore.now.sh/api/mscz?id=${this.id}&token=`