This is "minimal" in the sense that only the Authorization Code Flow
from OpenID Connect Core is implemented.  No discovery, no configuration
endpoint, and no user scope management.

OpenID Connect is an extension to the (already implemented) OAuth 2.0
protocol, and essentially an `id_token` JWT is added to the access token
endpoint response when using the Authorization Code Flow.  I also added
support for the "nonce" field since it is required to be used in the
id_token if the client decides to include it in its initial request.

In order to enable this extension an OAuth 2.0 scope containing
"openid" is needed. Other OAuth 2.0 requests should not be impacted by
this change.

This minimal implementation is enough to enable single sign-on (SSO)
for other sites, e.g. by using something like `mod_auth_openidc` to
only allow access to a CI server if a user has logged into Gitea.

Fixes: #1310

Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: zeripath <art27@cantab.net>

* remove github.com/unknwon/com from models

* dont use "com.ToStr()"

* replace "com.ToStr" with "fmt.Sprint" where its easy to do

* more refactor

* fix test

* just "proxy" Copy func for now

* as per @lunny

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

Following on from #11008 refactor UpdateOAuth2Application

* add API endpoint to create OAuth2 Application.

* move endpoint to /user. Add swagger documentations and proper response type.

* change json tags to snake_case. add CreateOAuth2ApplicationOptions to swagger docs.

* change response status to Created (201)

* add methods to list OAuth2 apps and delete an existing OAuth2 app by ID.

* add APIFormat convert method and file header

* fixed header

* hide secret on oauth2 application list

* add Created time to API response

* add API integration tests for create/list/delete OAuth2 applications.

Co-authored-by: techknowlogick <matti@mdranta.net>
Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: guillep2k <18600385+guillep2k@users.noreply.github.com>

Signed-off-by: Tamal Saha <tamal@appscode.com>

* display ui time with customize time location

* fix lint

* rename UILocation to DefaultUILocation

* move time related functions to modules/timeutil

* fix tests

* fix tests

* fix build

* fix swagger

* Add oauth2 grants ui

Signed-off-by: Jonas Franz <info@jonasfranz.software>

* Add delete functionality
Add translations

Signed-off-by: Jonas Franz <info@jonasfranz.software>

* Fix unit tests

Signed-off-by: Jonas Franz <info@jonasfranz.software>

* Fix unit tests

Signed-off-by: Jonas Franz <info@jonasfranz.software>

* Refactor DeleteOAuth2Grant
Use results.Close()

Signed-off-by: Jonas Franz <info@jonasfranz.software>

* Refactor DeleteOAuth2Grant (again)

Signed-off-by: Jonas Franz <info@jonasfranz.software>

* Check if user ID is zero

Signed-off-by: Jonas Franz <info@jonasfranz.software>

* Check if grant ID is zero

Signed-off-by: Jonas Franz <info@jonasfranz.software>