Airflow authentication setups fails with "AttributeError: can't set attribute" - airflow

Question

The Airflow version 1.8 password authentication setup as described in the docs fails at the step
user.password = 'set_the_password'
with error
AttributeError: can't set attribute

Answer 1

It's better to simply use the new method of PasswordUser _set_password:
# Instead of user.password = 'password'
user._set_password = 'password'

Answer 2

This is due to an update of SqlAlchemy to a version >= 1.2 that introduced a backwards incompatible change.
You can fix this by explicitly installing a SqlAlchemy version <1.2.
pip install 'sqlalchemy<1.2'
Or in a requirement.txt
sqlalchemy<1.2

Answer 3

Fixed with
pip install 'sqlalchemy<1.2'
I'm using apache-airflow 1.8.2

Answer 4

In case anyone's curious about what the incompatible change in SQLAlchemy 1.2 (mentioned in #DanT's answer) actually is, it is a change in how SQLAlchemy deals with hybrid proprerties. Beginning in 1.2, methods have to have the same name as the original hybrid, which was not required before. The fix for Airflow is very simple. The code in contrib/auth/backends/password_auth.py should change from this:
#password.setter
def _set_password(self, plaintext):
self._password = generate_password_hash(plaintext, 12)
if PY3:
self._password = str(self._password, 'utf-8')
to this:
#password.setter
def password(self, plaintext):
self._password = generate_password_hash(plaintext, 12)
if PY3:
self._password = str(self._password, 'utf-8')
See https://bitbucket.org/zzzeek/sqlalchemy/issues/4332/hybrid_property-gives-attributeerror for more details.