Because of new browser rules, I had to install local certificate authority and make localhost available via https for testing. I think it will be more common in the future. For using the locally-issued certificate, httplib2 has a parameter ca_certs; however, it cannot be available through pylti. I solved the problem with monkey patching; however, it seems awkward:

import httplib2
old_init = httplib2.Http.__init__
def new_init(self, *args, **kwargs):
    """Call the original __init__ function with the certificate."""
    old_init(self, *args, **kwargs, ca_certs=ROOT_CERTIFICATE_PATH)
httplib2.Http.__init__ = new_init

Maybe PYLTI_CONFIG could take ca_certs and pass to httplib2:

app.config['PYLTI_CONFIG'] = {
    'consumers': {CONSUMER_KEY: {'secret': CONSUMER_SECRET}},
    'ca_certs': ROOT_CERTIFICATE_PATH,
}