No refresh_token returned via OAuth 2.0 code grant flow

I am attempting an OAuth 2.0 code grant flow via electron native desktop client, using PKCE method to I am following the medium article titled: "Azure AD OAuth 2.0 Authorization Code Grant Flow in Electron"

I get an access_token, but not seeing a refresh token in the response: {"token_type":"Bearer","scope":"openid profile email https://graph.microsoft.com/User.Read","expires_in":3600,"ext_expires_in":3600,"access_token":"xxx"}