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>

services/auth/source/pam/assert_interface_test.go

@@ -0,0 +1,22 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package pam_test
+
+import (
+	"code.gitea.io/gitea/models"
+	"code.gitea.io/gitea/services/auth"
+	"code.gitea.io/gitea/services/auth/source/pam"
+)
+
+// This test file exists to assert that our Source exposes the interfaces that we expect
+// It tightly binds the interfaces and implementation without breaking go import cycles
+
+type sourceInterface interface {
+	auth.PasswordAuthenticator
+	models.LoginConfig
+	models.LoginSourceSettable
+}
+
+var _ (sourceInterface) = &pam.Source{}

services/auth/source/pam/source.go

@@ -0,0 +1,47 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package pam
+
+import (
+	"code.gitea.io/gitea/models"
+
+	jsoniter "github.com/json-iterator/go"
+)
+
+// __________  _____      _____
+// \______   \/  _  \    /     \
+//  |     ___/  /_\  \  /  \ /  \
+//  |    |  /    |    \/    Y    \
+//  |____|  \____|__  /\____|__  /
+//                  \/         \/
+
+// Source holds configuration for the PAM login source.
+type Source struct {
+	ServiceName string // pam service (e.g. system-auth)
+	EmailDomain string
+
+	// reference to the loginSource
+	loginSource *models.LoginSource
+}
+
+// FromDB fills up a PAMConfig from serialized format.
+func (source *Source) FromDB(bs []byte) error {
+	return models.JSONUnmarshalHandleDoubleEncode(bs, &source)
+}
+
+// ToDB exports a PAMConfig to a serialized format.
+func (source *Source) ToDB() ([]byte, error) {
+	json := jsoniter.ConfigCompatibleWithStandardLibrary
+	return json.Marshal(source)
+}
+
+// SetLoginSource sets the related LoginSource
+func (source *Source) SetLoginSource(loginSource *models.LoginSource) {
+	source.loginSource = loginSource
+}
+
+func init() {
+	models.RegisterLoginTypeConfig(models.LoginPAM, &Source{})
+}

services/auth/source/pam/source_authenticate.go

@@ -0,0 +1,62 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package pam
+
+import (
+	"fmt"
+	"strings"
+
+	"code.gitea.io/gitea/models"
+	"code.gitea.io/gitea/modules/auth/pam"
+	"code.gitea.io/gitea/modules/setting"
+
+	"github.com/google/uuid"
+)
+
+// Authenticate queries if login/password is valid against the PAM,
+// and create a local user if success when enabled.
+func (source *Source) Authenticate(user *models.User, login, password string) (*models.User, error) {
+	pamLogin, err := pam.Auth(source.ServiceName, login, password)
+	if err != nil {
+		if strings.Contains(err.Error(), "Authentication failure") {
+			return nil, models.ErrUserNotExist{Name: login}
+		}
+		return nil, err
+	}
+
+	if user != nil {
+		return user, nil
+	}
+
+	// Allow PAM sources with `@` in their name, like from Active Directory
+	username := pamLogin
+	email := pamLogin
+	idx := strings.Index(pamLogin, "@")
+	if idx > -1 {
+		username = pamLogin[:idx]
+	}
+	if models.ValidateEmail(email) != nil {
+		if source.EmailDomain != "" {
+			email = fmt.Sprintf("%s@%s", username, source.EmailDomain)
+		} else {
+			email = fmt.Sprintf("%s@%s", username, setting.Service.NoReplyAddress)
+		}
+		if models.ValidateEmail(email) != nil {
+			email = uuid.New().String() + "@localhost"
+		}
+	}
+
+	user = &models.User{
+		LowerName:   strings.ToLower(username),
+		Name:        username,
+		Email:       email,
+		Passwd:      password,
+		LoginType:   models.LoginPAM,
+		LoginSource: source.loginSource.ID,
+		LoginName:   login, // This is what the user typed in
+		IsActive:    true,
+	}
+	return user, models.CreateUser(user)
+}