We have tried to found another ways to post on Google+ but don't got any solution because Google+ is providing higher securty for writing permission.
Google+ default providing permission which is read permission and using our regular google account we can easily do it but we want to post on Google+ so we'll need google permission and for permission we'll need to create google domain account.
Please check this note which is google said:
Important: The access.domainRestricted property must be set to true for posts using the Google+ Domains API. Posts in Google+ are private by default so you must also specify the access.items property to choose the audience within the domain that is authorized to view the post.
And grant permissions which is google also said:
Required - Grants permission for the app to create posts or comments on behalf of a user. The Google+ Domains API only allows creation of restricted posts, and only allows comments to be added to restricted posts.
You can check these bellows links :
https://developers.google.com/+/domains/posts/creating
https://support.google.com/plus/answer/2705802 https://developers.google.com/+/domains/api/activities/insert#auth
https://developers.google.com/+/domains/authentication/scopes
https://developers.google.com/+/domains/api/activities/insert