Afaik, adding these lines does nothing unless the file(s) are present. Having them in let's admins supply certs instead of relying on TOFU.

Co-authored-by: zeripath <art27@cantab.net>

* Add ssh certificate support

* Add ssh certificate support to builtin ssh

* Write trusted-user-ca-keys.pem based on configuration

* Update app.example.ini

* Update templates/user/settings/keys_principal.tmpl

Co-authored-by: silverwind <me@silverwind.io>

* Remove unused locale string

* Update options/locale/locale_en-US.ini

Co-authored-by: silverwind <me@silverwind.io>

* Update options/locale/locale_en-US.ini

Co-authored-by: silverwind <me@silverwind.io>

* Update models/ssh_key.go

Co-authored-by: silverwind <me@silverwind.io>

* Add missing creation of SSH.Rootpath

* Update cheatsheet, example and locale strings

* Update models/ssh_key.go

Co-authored-by: zeripath <art27@cantab.net>

* Update models/ssh_key.go

Co-authored-by: zeripath <art27@cantab.net>

* Update models/ssh_key.go

Co-authored-by: zeripath <art27@cantab.net>

* Update models/ssh_key.go

Co-authored-by: zeripath <art27@cantab.net>

* Update models/ssh_key.go

* Optimizations based on feedback

* Validate CA keys for external sshd

* Add filename option and change default filename

Add a SSH_TRUSTED_USER_CA_KEYS_FILENAME option which default is
RUN_USER/.ssh/gitea-trusted-user-ca-keys.pem

Do not write a file when SSH_TRUSTED_USER_CA_KEYS is empty.

Add some more documentation.

* Remove unneeded principalkey functions

* Add blank line

* Apply suggestions from code review

Co-authored-by: zeripath <art27@cantab.net>

* Add SSH_AUTHORIZED_PRINCIPALS_ALLOW option

This adds a SSH_AUTHORIZED_PRINCIPALS_ALLOW which is default
email,username this means that users only can add the principals
that match their email or username.

To allow anything the admin need to set the option anything.

This allows for a safe default in gitea which protects against malicious
users using other user's prinicipals. (before that user could set it).

This commit also has some small other fixes from the last code review.

* Rewrite principal keys file on user deletion

* Use correct rewrite method

* Set correct AuthorizedPrincipalsBackup default setting

* Rewrite principalsfile when adding principals

* Add update authorized_principals option to admin dashboard

* Handle non-primary emails

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Add the command actually to the dashboard template

* Update models/ssh_key.go

Co-authored-by: silverwind <me@silverwind.io>

* By default do not show principal options unless there are CA keys set or they are explicitly set

Signed-off-by: Andrew Thornton <art27@cantab.net>

* allow settings when enabled

* Fix typos in TrustedUserCAKeys path

* Allow every CASignatureAlgorithms algorithm

As this depends on the content of TrustedUserCAKeys we should allow all
signature algorithms as admins can choose the specific algorithm on their
signing CA

* Update models/ssh_key.go

Co-authored-by: Lauris BH <lauris@nix.lv>

* Fix linting issue

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: Lauris BH <lauris@nix.lv>
Co-authored-by: techknowlogick <matti@mdranta.net>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>

* Disable DSA ssh keys by default

OpenSSH has disabled DSA keys since version 7.0

As the docker runs openssh > v7.0 we should just disable
DSA keys by default.

Refers to #11417

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Just disable DSA keys by default

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Appears we need to set the minimum key sizes too

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Appears we need to set the minimum key sizes too

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Remove DSA type

* Fix Tests

Co-authored-by: techknowlogick <techknowlogick@gitea.io>
Co-authored-by: Lauris BH <lauris@nix.lv>

docker/root/usr/bin/entrypoint already allows for the specification
of USER, USER_UID, USER_GID. But since AllowedUsers is hardcoded in
sshd_config, one cannot log in as a user different ftom git.
This change substitutes ${USER} for git in the sshd_config template.

Signed-off-by: Jeronimo Pellegrini <j_p@aleph0.info>

* - rearrange the templates to make it more logical because now ssh_config is a template
- implemented the updating of the port to the same as the port sent to the gitea config

* change the filename back