diff --git a/index.ts b/index.ts
index 45cd8ed3..e17ad26c 100755
--- a/index.ts
+++ b/index.ts
@@ -60,14 +60,16 @@ commander
  * Logs the user in. Saves the client credentials to an rc file.
  * @name login
  * @param {string?} [--no-localhost] Do not run a local server, manually enter code instead.
- * @param {string?} [--ownkey] Save .clasprc.json file to current working directory.
+ * @param {string?} [--creds] Relative path to credentials (from GCP).
+ * @example login (uses default clasp credentials)
+ * @example login --creds credentials.json (uses your credentials file).
  * @see test
  */
 commander
   .command('login')
   .description('Log in to script.google.com')
   .option('--no-localhost', 'Do not run a local server, manually enter code instead')
-  .option('--ownkey', 'Save .clasprc.json file to current working directory')
+  .option('--creds <file>', 'Relative path to credentials (from GCP).')
   .action(login);
 
 /**
diff --git a/src/auth.ts b/src/auth.ts
index 60e707ed..6a1c932b 100644
--- a/src/auth.ts
+++ b/src/auth.ts
@@ -12,6 +12,7 @@ import { Script } from 'googleapis/build/src/apis/script/v1';
 import { ClaspSettings, DOTFILE, ERROR, LOG, checkIfOnline, logError } from './utils';
 import open = require('open');
 import readline = require('readline');
+import * as fs from 'fs';
 
 // API settings
 // @see https://developers.google.com/oauthplayground/
@@ -32,7 +33,7 @@ const oauth2ClientSettings = {
   clientSecret: 'v6V3fKV_zWU7iw1DrpO1rknX',
   redirectUri: 'http://localhost',
 };
-export const oauth2Client = new OAuth2Client(oauth2ClientSettings);
+const oauth2Client = new OAuth2Client(oauth2ClientSettings);
 
 // Google API clients
 export const script = google.script({
@@ -52,11 +53,30 @@ export const drive = google.drive({
  * Requests authorization to manage Apps Script projects.
  * @param {boolean} useLocalhost True if a local HTTP server should be run
  *     to handle the auth response. False if manual entry used.
+ * @param {string} creds location of credentials file.
  */
-async function authorize(useLocalhost: boolean, writeToOwnKey: boolean) {
+async function authorize(useLocalhost: boolean, creds: string) {
+  let ownCreds = false;
+  try {
+    const credentials = JSON.parse(fs.readFileSync(creds, 'utf8'));
+    if (credentials && credentials.installed && credentials.installed.client_id
+      && credentials.installed.client_secret) {
+        oauth2ClientSettings.clientId = credentials.installed.client_id;
+        oauth2ClientSettings.clientSecret = credentials.installed.client_secret;
+        ownCreds = true;
+        console.log(LOG.CREDENTIALS_FOUND);
+    } else {
+      logError(null, ERROR.BAD_CREDENTIALS_FILE);
+    }
+  } catch(err) {
+    if (err.code === 'ENOENT') {
+      logError(null, ERROR.CREDENTIALS_DNE);
+    }
+    console.log(LOG.DEFAULT_CREDENTIALS);
+  }
   try {
     const token = await (useLocalhost ? authorizeWithLocalhost() : authorizeWithoutLocalhost());
-    await (writeToOwnKey ? DOTFILE.RC_LOCAL.write(token) : DOTFILE.RC.write(token));
+    await (ownCreds ? DOTFILE.RC_LOCAL.write(token) : DOTFILE.RC.write(token));
     console.log(LOG.AUTH_SUCCESSFUL);
     process.exit(0); // gracefully exit after successful login
   } catch(err) {
@@ -141,9 +161,11 @@ async function authorizeWithoutLocalhost() {
 
 /**
  * Logs the user in. Saves the client credentials to an rc file.
- * @param options the localhost and ownkey options from commander
+ * @param {object} options the localhost and creds options from commander.
+ * @param {boolean} options.localhost authorize without http server.
+ * @param {string} options.creds location of credentials file.
  */
-export function login(options: { localhost: boolean, ownkey: boolean}) {
+export function login(options: { localhost: boolean, creds: string}) {
   DOTFILE.RC.read().then((rc: ClaspSettings) => {
     console.warn(ERROR.LOGGED_IN);
   }).catch(async (err: string) => {
@@ -151,7 +173,7 @@ export function login(options: { localhost: boolean, ownkey: boolean}) {
       console.warn(ERROR.LOGGED_IN);
     }).catch(async (err: string) => {
       await checkIfOnline();
-      authorize(options.localhost, options.ownkey);
+      authorize(options.localhost, options.creds);
     });
   });
 }
\ No newline at end of file
diff --git a/src/utils.ts b/src/utils.ts
index 27a6c091..c80d2a4a 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -81,10 +81,12 @@ export const DOTFILE = {
 // Error messages (some errors take required params)
 export const ERROR = {
   ACCESS_TOKEN: `Error retrieving access token: `,
+  BAD_CREDENTIALS_FILE: 'Incorrect credentials file format.',
   COMMAND_DNE: (command: string) => `🤔  Unknown command "${command}"\n
 Forgot ${PROJECT_NAME} commands? Get help:\n  ${PROJECT_NAME} --help`,
   CONFLICTING_FILE_EXTENSION: (name: string) => `File names: ${name}.js/${name}.gs conflict. Only keep one.`,
   CREATE: 'Error creating script.',
+  CREDENTIALS_DNE: 'Credentials file not found.',
   DEPLOYMENT_COUNT: `Unable to deploy; Scripts may only have up to 20 versioned deployments at a time.`,
   FOLDER_EXISTS: `Project file (${DOT.PROJECT.PATH}) already exists.`,
   FS_DIR_WRITE: 'Could not create directory.',
@@ -120,6 +122,8 @@ export const LOG = {
   CLONING: 'Cloning files...',
   CREATE_PROJECT_FINISH: (scriptId: string) => `Created new script: ${getScriptURL(scriptId)}`,
   CREATE_PROJECT_START: (title: string) => `Creating new script: ${title}...`,
+  CREDENTIALS_FOUND: 'Credentials found, using those to login...',
+  DEFAULT_CREDENTIALS: 'No credentials given, continuing with default...',
   DEPLOYMENT_CREATE: 'Creating deployment...',
   DEPLOYMENT_DNE: 'No deployed versions of script.',
   DEPLOYMENT_LIST: (scriptId: string) => `Listing deployments...`,