single sign on for api access

You can use the Authorization Code Flow which you don't need to pass in your password. 

Read the documentation and write code. You can reference code here: 

Step 1: build an authorize uri: https://github.com/tylerlong/ringcentral-python/blob/master/ringcentral_client/rest_client.py#L73-L8...
Step 2: redirect user to authorized uri in browser
Step 3: when user is redirected back, you will be able to get an auth_code, invoke this: https://github.com/tylerlong/ringcentral-python/blob/master/ringcentral_client/rest_client.py#L35-L4...

Please note that, code sample above is from an UNOFFICIAL python SDK. The official one doesn't have any helper methods for authorization code flow.

Here is a tutorial in Node for your reference: https://ringcentral-tutorials.github.io/authorization-code-flow-nodejs-express-demo/