Read emails from Gmail API using Node.js and Postman

Example response of API call
https://www.postman.com/collections/6655f0c79fe567dd58fc

Other reading
https://www.labnol.org/google-api-service-account-220405
https://medium.com/@sirajul.anik/understanding-oauth-2-0-179543b18bd

Original packages from google API doc (more complicated solutions)
https://www.npmjs.com/package/googleapis
https://www.npmjs.com/package/@google-cloud/local-auth

Packages that have simple usages than google API docs
https://github.com/SpiderStrategies/node-gmail-api
https://github.com/jaredhanson/passport-google-oauth

Pre studies

OAuth 2.0

https://oauth.net/2/
Important flows

• Protocol Flow
• Refreshing an Expired Access Token
• Authorization Code Flow

Using OAuth 2.0 to Access Google APIs

https://developers.google.com/identity/protocols/oauth2

Gmail API Overview

https://developers.google.com/gmail/api/guides

Node.js quickstart

https://developers.google.com/gmail/api/quickstart/nodejs

Codes implementation examples in JavaScript

authenticate

To get an access token using OAuth 2.0 Client ID (Desktop application)

• Change the scopes into Gmail API scope
  ​​​​const SCOPES = ['https://www.googleapis.com/auth/gmail.readonly'];
  

• Here use a file to store the credential, better to store them as secrets in the config file of the project

Get Gmail API access token

https://www.daimto.com/how-to-get-a-google-access-token-with-curl/

https://wiki.genexus.com/commwiki/servlet/wiki?50408,Google+OAuth+2.0+process+for+emails%3A+Generation+and+data+collection+by+the+Administrator

1. Get Authorization Code

Request type

GET

Request URL (Need to open it in browser)

https://accounts.google.com/o/oauth2/v2/auth?access_type={{access_type}}&scope={{scopes}}&client_id={{client_id}}&redirect_uri={{redirectURL}}&response_type={{response_type}}

Query strings and their values

Query string	Value
access_type	offline
scope	https://mail.google.com/
client_id	The created OAuth 2.0 Client ID client id
redirect_uri	urn:ietf:wg:oauth:2.0:oob
response_type	code

In Postman

For viewing only, since the get code steps need manual work in the browser

2. Get refresh token and access token

Use authorization code, only need to run this step at first time, can store and reuse the refresh token.

Request type

POST

Request URL

https://accounts.google.com/o/oauth2/token?code={{authorization_code}}&client_id={{client_id}}&client_secret={{client_secret}}&redirect_uri={{redirect_uri}}&grant_type={{grant_type}}

Query strings and their values

Query string	Value
code	The Authorization code from step 1. Get Authorization Code
client_id	The created OAuth 2.0 Client ID client id
client_secret	The created OAuth 2.0 Client ID client secret
redirect_uri	urn:ietf:wg:oauth:2.0:oob
grant_type	authorization_code

Response

• Contains both refresh token and access token
• Save the refresh token from the response
  

3. Get access token using the refresh token

Request type

POST

Request URL (Need to open it in browser)

https://accounts.google.com/o/oauth2/token?refresh_token={{refresh_token}}&client_id={{client_id}}&client_secret={{client_secret}}&redirect_uri={{redirect_uri}}&grant_type={{grant_type_refresh_token}}

Query strings and their values

Query string	Value
refresh_token	The refresh token from step 2. Get refresh token and access token
client_id	The created OAuth 2.0 Client ID client id
client_secret	The created OAuth 2.0 Client ID client secret
redirect_uri	urn:ietf:wg:oauth:2.0:oob
grant_type	refresh_token

In Postman

Use the access token from the response to access Gmail API

4. Example usage: Get messages from Gmail

Resources
https://www.postman.com/api-evangelist/workspace/google/collection/35240-0d073c40-6ad8-43d0-8baf-8ee3606819e0?ctx=documentation

https://mailtrap.io/blog/send-emails-with-gmail-api/

Request type

GET

Request URL

https://gmail.googleapis.com/gmail/v1/users/{{user_id}}/messages

user_id
The testing user gmail that is saved in OAuth consent screen, for example, [e-mail]

In Postman

Set the Authorization type of the request to Bearer Token (which is the access token from step 3. Get access token using the refresh token)

Error handling

1. "Error 403: access_denied" when getting Authorization Code

Solution
https://stackoverflow.com/questions/73062345/error-403-access-denied-when-usign-google-oauth

Add a testing user gmail and save (which will be the test account that accesses the Gmail API), for example, [e-mail]

After adding the testing user, and choosing the authorization account again, click Continue after seeing:

And keep clicking Continue

Finally copy and save the Authorization Code that shows in the browser

2. Seeing Invalid_grant, Bad Request when getting refresh token

Solution
Do step 1. Get Authorization Code again to get a new Authorization Code, and use the new Authorization Code to get the refresh token by doing step 2. Get refresh token and access token.

tags: api testing test automation software test