Refactor: Move login out of models (#16199)

`models` does far too much. In particular it handles all `UserSignin`.

It shouldn't be responsible for calling LDAP, SMTP or PAM for signing in.

Therefore we should move this code out of `models`.

This code has to depend on `models` - therefore it belongs in `services`.

There is a package in `services` called `auth` and clearly this functionality belongs in there.

Plan:

- [x] Change `auth.Auth` to `auth.Method` - as they represent methods of authentication.
- [x] Move `models.UserSignIn` into `auth`
- [x] Move `models.ExternalUserLogin`
- [x] Move most of the `LoginVia*` methods to `auth` or subpackages
- [x] Move Resynchronize functionality to `auth`
  - Involved some restructuring of `models/ssh_key.go` to reduce the size of this massive file and simplify its files.
- [x] Move the rest of the LDAP functionality in to the ldap subpackage
- [x] Re-factor the login sources to express an interfaces `auth.Source`?
  - I've done this through some smaller interfaces Authenticator and Synchronizable - which would allow us to extend things in future
- [x] Now LDAP is out of models - need to think about modules/auth/ldap and I think all of that functionality might just be moveable
- [x] Similarly a lot Oauth2 functionality need not be in models too and should be moved to services/auth/source/oauth2
  - [x] modules/auth/oauth2/oauth2.go uses xorm... This is naughty - probably need to move this into models.
  - [x] models/oauth2.go - mostly should be in modules/auth/oauth2 or services/auth/source/oauth2 
- [x] More simplifications of login_source.go may need to be done
- Allow wiring in of notify registration -  *this can now easily be done - but I think we should do it in another PR*  - see #16178 
- More refactors...?
  - OpenID should probably become an auth Method but I think that can be left for another PR
  - Methods should also probably be cleaned up  - again another PR I think.
  - SSPI still needs more refactors.* Rename auth.Auth auth.Method
* Restructure ssh_key.go

- move functions from models/user.go that relate to ssh_key to ssh_key
- split ssh_key.go to try create clearer function domains for allow for
future refactors here.

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

routers/web/user/auth.go

@@ -14,7 +14,6 @@ import (
 	"strings"
 
 	"code.gitea.io/gitea/models"
-	"code.gitea.io/gitea/modules/auth/oauth2"
 	"code.gitea.io/gitea/modules/base"
 	"code.gitea.io/gitea/modules/context"
 	"code.gitea.io/gitea/modules/eventsource"
@@ -27,6 +26,8 @@ import (
 	"code.gitea.io/gitea/modules/web"
 	"code.gitea.io/gitea/modules/web/middleware"
 	"code.gitea.io/gitea/routers/utils"
+	"code.gitea.io/gitea/services/auth"
+	"code.gitea.io/gitea/services/auth/source/oauth2"
 	"code.gitea.io/gitea/services/externalaccount"
 	"code.gitea.io/gitea/services/forms"
 	"code.gitea.io/gitea/services/mailer"
@@ -135,7 +136,7 @@ func SignIn(ctx *context.Context) {
 		return
 	}
 
-	orderedOAuth2Names, oauth2Providers, err := models.GetActiveOAuth2Providers()
+	orderedOAuth2Names, oauth2Providers, err := oauth2.GetActiveOAuth2Providers()
 	if err != nil {
 		ctx.ServerError("UserSignIn", err)
 		return
@@ -155,7 +156,7 @@ func SignIn(ctx *context.Context) {
 func SignInPost(ctx *context.Context) {
 	ctx.Data["Title"] = ctx.Tr("sign_in")
 
-	orderedOAuth2Names, oauth2Providers, err := models.GetActiveOAuth2Providers()
+	orderedOAuth2Names, oauth2Providers, err := oauth2.GetActiveOAuth2Providers()
 	if err != nil {
 		ctx.ServerError("UserSignIn", err)
 		return
@@ -174,7 +175,7 @@ func SignInPost(ctx *context.Context) {
 	}
 
 	form := web.GetForm(ctx).(*forms.SignInForm)
-	u, err := models.UserSignIn(form.UserName, form.Password)
+	u, err := auth.UserSignIn(form.UserName, form.Password)
 	if err != nil {
 		if models.IsErrUserNotExist(err) {
 			ctx.RenderWithErr(ctx.Tr("form.username_password_incorrect"), tplSignIn, &form)
@@ -577,13 +578,13 @@ func SignInOAuth(ctx *context.Context) {
 		return
 	}
 
-	if err = oauth2.Auth(loginSource.Name, ctx.Req, ctx.Resp); err != nil {
+	if err = loginSource.Cfg.(*oauth2.Source).Callout(ctx.Req, ctx.Resp); err != nil {
 		if strings.Contains(err.Error(), "no provider for ") {
-			if err = models.ResetOAuth2(); err != nil {
+			if err = oauth2.ResetOAuth2(); err != nil {
 				ctx.ServerError("SignIn", err)
 				return
 			}
-			if err = oauth2.Auth(loginSource.Name, ctx.Req, ctx.Resp); err != nil {
+			if err = loginSource.Cfg.(*oauth2.Source).Callout(ctx.Req, ctx.Resp); err != nil {
 				ctx.ServerError("SignIn", err)
 			}
 			return
@@ -631,7 +632,7 @@ func SignInOAuthCallback(ctx *context.Context) {
 			}
 			if len(missingFields) > 0 {
 				log.Error("OAuth2 Provider %s returned empty or missing fields: %s", loginSource.Name, missingFields)
-				if loginSource.IsOAuth2() && loginSource.OAuth2().Provider == "openidConnect" {
+				if loginSource.IsOAuth2() && loginSource.Cfg.(*oauth2.Source).Provider == "openidConnect" {
 					log.Error("You may need to change the 'OPENID_CONNECT_SCOPES' setting to request all required fields")
 				}
 				err = fmt.Errorf("OAuth2 Provider %s returned empty or missing fields: %s", loginSource.Name, missingFields)
@@ -772,8 +773,7 @@ func handleOAuth2SignIn(ctx *context.Context, u *models.User, gothUser goth.User
 // OAuth2UserLoginCallback attempts to handle the callback from the OAuth2 provider and if successful
 // login the user
 func oAuth2UserLoginCallback(loginSource *models.LoginSource, request *http.Request, response http.ResponseWriter) (*models.User, goth.User, error) {
-	gothUser, err := oauth2.ProviderCallback(loginSource.Name, request, response)
-
+	gothUser, err := loginSource.Cfg.(*oauth2.Source).Callback(request, response)
 	if err != nil {
 		if err.Error() == "securecookie: the value is too long" {
 			log.Error("OAuth2 Provider %s returned too long a token. Current max: %d. Either increase the [OAuth2] MAX_TOKEN_LENGTH or reduce the information returned from the OAuth2 provider", loginSource.Name, setting.OAuth2.MaxTokenLength)
@@ -901,7 +901,7 @@ func LinkAccountPostSignIn(ctx *context.Context) {
 		return
 	}
 
-	u, err := models.UserSignIn(signInForm.UserName, signInForm.Password)
+	u, err := auth.UserSignIn(signInForm.UserName, signInForm.Password)
 	if err != nil {
 		if models.IsErrUserNotExist(err) {
 			ctx.Data["user_exists"] = true