oAuth2 login to Vault

[Dabami]

I have a problem with the oAuth2 extension.
I'm working with Connector version 0.10.0 and I'm trying to get a token from a Hashicorp Vault (/v1/auth/approle/login). The dataplane is making a request to the Vault token URL with proper credentials, but its getting the following error:

{
    "errors": [
        "failed to determine alias name from login request"
    ]
}

With postman I realized that this error raises when the 'Content-length' header is missing. I managed to debug the code of the oAuth2 extension and I noticed that this header is not set on the request. At this point, I don't know whats the best way to proceed. How can I solve this situation without modifying extension's code?
Thanks in advance.

Edit: I'm working with a Dockerized version of the MVD.