Do not double-decode username and password in SQLAlchemy URL

[arpitjain099]

Description

When connecting through SQLAlchemy, a password that contains a literal + was being corrupted into a space, which then failed authentication with a 401. The cause is a double decode: SQLAlchemy's make_url() already percent-decodes the userinfo, and create_connect_args then ran url.username and url.password through unquote_plus a second time. unquote_plus follows the form-encoding rule where + means space, but that rule only applies to the query string, not to the userinfo, so pass+word became pass word.

The fix uses url.username and url.password directly since SQLAlchemy has already decoded them. This mirrors what SQLAlchemy itself did for the same problem (see sqlalchemy/sqlalchemy#2873). The unquote_plus calls on the query parameters are intentionally left as-is, because there + really does mean space and the values are not form-decoded by SQLAlchemy.

I added a regression test with + in both the username and password, and the full tests/unit/sqlalchemy/test_dialect.py suite passes (19 tests). Closes #611.

Non-technical explanation

Passwords with a plus sign in them now work when you connect using a SQLAlchemy URL, instead of failing to log in.

Release notes

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* Fix SQLAlchemy authentication failing for usernames or passwords that contain a `+` character. ({issue}`611`)