Write access to a repo on Bitbucket using SSH keys

[Niranjan Manjunath]

I have a requirement where from a Bitbucket pipeline of a private Repo A, I would like to checkout Repo B, make changes and push to Repo B from within the build pipeline of Repo A. 

If I use the SSH keypair to establish authentication, looks like Repo A is only authorized to do read only operation (checkout)

+ git push origin devWarning: Permanently added the RSA host key for IP address '18.205.93.0' to the list of known hosts.Unauthorizedfatal: Could not read from remote repository.Please make sure you have the correct access rightsand the repository exists.

How can I acheive this without having to create an additional user on Bitbucket with the privileges just to do this?

Thank you for your time.