cc_ssh: parse_ssh_config_map does not take into account user-specific Match section overrides

This bug was originally filed in Launchpad as [LP: #1935857](https://bugs.launchpad.net/cloud-init/+bug/1935857)

Launchpad details

affected_projects = []

assignee = None

assignee_name = None

date_closed = None

date_created = 2021-07-12T17:55:13.369080+00:00

date_fix_committed = None

date_fix_released = None

id = 1935857

importance = low

is_complete = False

lp_url = https://bugs.launchpad.net/cloud-init/+bug/1935857

milestone = None

owner = chad.smith

owner_name = Chad Smith

private = False

status = triaged

submitter = chad.smith

submitter_name = Chad Smith

tags = []

duplicates = []

_Launchpad user **Chad Smith(chad.smith)** wrote on 2021-07-12T17:55:13.369080+00:00_

cloud-init 21.2

User-specific Match sections can be provided in /etc/ssh/sshd_config to override global ssh config default settings such as AuthorizedKeysFile.

cloud-init's parsing of sshd_config in ssh_util[1] is simplistic and treats each line in the sshd_config file as simple key/value pairs. Any Match sections defined below a global AuthorizedKeysFile setting will be overridden to the line containing an AuthorizedKeysFile definition, even if that definition should only be scoped to a specific user Match.

Here is an example adding a specific Match section which should only apply non-default AuthorizedKeysFile to the "custom" user, and how cloud-init incorrectly represents that content.

$ cat sshd_bad_parse.yaml <