pynfs: rpc AuthGss.init_cred fails on missing attrs/wrong usage of gssapi (nfs4 client)

Using the latest pynfs (from git) with python-gssapi 0.6.4.
Trying to test NFS4 client with flavor=rpc.RPCSEC_GSS from python:

opts=...
opts.flavor=rpc.RPCSEC_GSS
self.env = environment.Environment(opts)

Getting 'AttributeError' from different places.

Stack trace1:
nfs4/nfs4_client.py:61: in __init__
    self.env = environment.Environment(opts)
lib/python3.6/site-packages/nfs4/server41tests/environment.py:128: in __init__
    krb5_cred = AuthGss().init_cred(call, target="nfs@%s" % opts.server)
lib/python3.6/site-packages/rpc/security.py:249: AttributeError

      target = gssapi.Name(target, gssapi.NT_HOSTBASED_SERVICE)

E       AttributeError: module 'gssapi' has no attribute 'NT_HOSTBASED_SERVICE'

For this error, in python-gssapi-0.6.4/gssapi/__init__.py I see that
correct name for this attribute is 'C_NT_HOSTBASED_SERVICE' (not
'NT_HOSTBASED_SERVICE'):
C_NT_HOSTBASED_SERVICE = bindings.C.GSS_C_NT_HOSTBASED_SERVICE

Stack trace2:
nfs4/nfs4_client.py:61: in __init__
    self.env = environment.Environment(opts)
lib/python3.6/site-packages/nfs4/server41tests/environment.py:128: in __init__
    krb5_cred = AuthGss().init_cred(call, target="nfs@%s" % opts.server)
lib/python3.6/site-packages/rpc/security.py:267: AttributeError

          token = context.init(target, token, gss_cred)

E           AttributeError: 'Context' object has no attribute 'init'

For this error, in python-gssapi-0.6.4/gssapi/ctx.py file I see that the
'Context' class __init__ method has no parameters, init() method is
really missing.

I suspect that python-gssapi was changed or I'm using the wrong
version/code of the gssapi library.
I tried to use the old gssapi lib version (before fork) -
gssapi-1.6.13 - but I get similar errors.
'README' file for pynfs says that we need the 'python3-gssapi'
package, but it is missing in the repository, so I have to install it
manually.

Please advise what gssapi python library version is proven to work with pynfs.
Thanks!