diff --git a/lib/authutil.js b/lib/authutil.js
index 96839fc5..1000a91f 100644
--- a/lib/authutil.js
+++ b/lib/authutil.js
@@ -1,12 +1,4 @@
 "use strict";
-var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, generator) {
-    return new (P || (P = Promise))(function (resolve, reject) {
-        function fulfilled(value) { try { step(generator.next(value)); } catch (e) { reject(e); } }
-        function rejected(value) { try { step(generator["throw"](value)); } catch (e) { reject(e); } }
-        function step(result) { result.done ? resolve(result.value) : new P(function (resolve) { resolve(result.value); }).then(fulfilled, rejected); }
-        step((generator = generator.apply(thisArg, _arguments || [])).next());
-    });
-};
 var __importStar = (this && this.__importStar) || function (mod) {
     if (mod && mod.__esModule) return mod;
     var result = {};
@@ -15,28 +7,38 @@ var __importStar = (this && this.__importStar) || function (mod) {
     return result;
 };
 Object.defineProperty(exports, "__esModule", { value: true });
-const core = __importStar(require("@actions/core"));
+const fs = __importStar(require("fs"));
+const os = __importStar(require("os"));
 const path = __importStar(require("path"));
-const exec = __importStar(require("@actions/exec"));
+const core = __importStar(require("@actions/core"));
 function configAuth(registryUrl) {
-    return __awaiter(this, void 0, void 0, function* () {
-        let npmrc = path.resolve(process.cwd(), '.npmrc');
-        let yarnrc = path.resolve(process.cwd(), '.yarnrc');
-        yield writeRegistryToFile(registryUrl, 'npm', 'NPM_TOKEN');
-        // writeRegistryToFile(registryUrl, 'yarn', 'YARN_TOKEN');
-    });
+    let npmrc = path.resolve(process.cwd(), '.npmrc');
+    let yarnrc = path.resolve(process.cwd(), '.yarnrc');
+    writeRegistryToFile(registryUrl, npmrc, 'NPM_TOKEN');
+    writeRegistryToFile(registryUrl, yarnrc, 'YARN_TOKEN');
 }
 exports.configAuth = configAuth;
-function writeRegistryToFile(registryUrl, packageManager, authTokenName) {
-    return __awaiter(this, void 0, void 0, function* () {
-        core.debug(`Setting up ${packageManager} auth`);
-        yield exec.exec(`${packageManager} config set registry=${registryUrl}`);
-        yield exec.exec(`${packageManager} config set always-auth=true`);
-        yield exec.exec(packageManager +
-            ' config set ' +
+function writeRegistryToFile(registryUrl, fileLocation, authTokenName) {
+    core.debug(`Setting auth in ${fileLocation}`);
+    let newContents = '';
+    if (fs.existsSync(fileLocation)) {
+        const curContents = fs.readFileSync(fileLocation, 'utf8');
+        curContents.split(os.EOL).forEach((line) => {
+            // Add current contents unless they are setting the registry
+            if (!line.startsWith('registry')) {
+                newContents += line + os.EOL;
+            }
+        });
+    }
+    newContents +=
+        'registry=' +
+            registryUrl +
+            os.EOL +
+            'always-auth=true' +
+            os.EOL +
             registryUrl.replace(/(^\w+:|^)/, '') +
-            ':_authToken ${' +
+            ':_authToken=${' +
             authTokenName +
-            '}');
-    });
+            '}';
+    fs.writeFileSync(fileLocation, newContents);
 }
diff --git a/lib/setup-node.js b/lib/setup-node.js
index 2ecfd685..26d716a4 100644
--- a/lib/setup-node.js
+++ b/lib/setup-node.js
@@ -33,7 +33,7 @@ function run() {
             }
             const registryUrl = core.getInput('registry-url');
             if (registryUrl) {
-                yield auth.configAuth(registryUrl);
+                auth.configAuth(registryUrl);
             }
             // TODO: setup proxy from runner proxy config
             const matchersPath = path.join(__dirname, '..', '.github');
diff --git a/src/authutil.ts b/src/authutil.ts
index 5e3ee6fa..503a3e14 100644
--- a/src/authutil.ts
+++ b/src/authutil.ts
@@ -1,29 +1,41 @@
-import * as core from '@actions/core';
+import * as fs from 'fs';
+import * as os from 'os';
 import * as path from 'path';
-import * as exec from '@actions/exec';
+import * as core from '@actions/core';
 
-export async function configAuth(registryUrl: string) {
+export function configAuth(registryUrl: string) {
   let npmrc: string = path.resolve(process.cwd(), '.npmrc');
   let yarnrc: string = path.resolve(process.cwd(), '.yarnrc');
 
-  await writeRegistryToFile(registryUrl, 'npm', 'NPM_TOKEN');
-  // writeRegistryToFile(registryUrl, 'yarn', 'YARN_TOKEN');
+  writeRegistryToFile(registryUrl, npmrc, 'NPM_TOKEN');
+  writeRegistryToFile(registryUrl, yarnrc, 'YARN_TOKEN');
 }
 
-async function writeRegistryToFile(
+function writeRegistryToFile(
   registryUrl: string,
-  packageManager: string,
+  fileLocation: string,
   authTokenName: string
 ) {
-  core.debug(`Setting up ${packageManager} auth`);
-  await exec.exec(`${packageManager} config set registry=${registryUrl}`);
-  await exec.exec(`${packageManager} config set always-auth=true`);
-  await exec.exec(
-    packageManager +
-      ' config set ' +
-      registryUrl.replace(/(^\w+:|^)/, '') +
-      ':_authToken ${' +
-      authTokenName +
-      '}'
-  );
+  core.debug(`Setting auth in ${fileLocation}`);
+  let newContents = '';
+  if (fs.existsSync(fileLocation)) {
+    const curContents = fs.readFileSync(fileLocation, 'utf8');
+    curContents.split(os.EOL).forEach((line: string) => {
+      // Add current contents unless they are setting the registry
+      if (!line.startsWith('registry')) {
+        newContents += line + os.EOL;
+      }
+    });
+  }
+  newContents +=
+    'registry=' +
+    registryUrl +
+    os.EOL +
+    'always-auth=true' +
+    os.EOL +
+    registryUrl.replace(/(^\w+:|^)/, '') +
+    ':_authToken=${' +
+    authTokenName +
+    '}';
+  fs.writeFileSync(fileLocation, newContents);
 }
diff --git a/src/setup-node.ts b/src/setup-node.ts
index c15c8cff..c0387861 100644
--- a/src/setup-node.ts
+++ b/src/setup-node.ts
@@ -17,7 +17,7 @@ async function run() {
 
     const registryUrl = core.getInput('registry-url');
     if (registryUrl) {
-      await auth.configAuth(registryUrl);
+      auth.configAuth(registryUrl);
     }
 
     // TODO: setup proxy from runner proxy config