[chore] The Big Middleware and API Refactor (tm) (#1250)

* interim commit: start refactoring middlewares into package under router

* another interim commit, this is becoming a big job

* another fucking massive interim commit

* refactor bookmarks to new style

* ambassador, wiz zeze commits you are spoiling uz

* she compiles, we're getting there

* we're just normal men; we're just innocent men

* apiutil

* whoopsie

* i'm glad noone reads commit msgs haha :blob_sweat:

* use that weirdo go-bytesize library for maxMultipartMemory

* fix media module paths

internal/api/auth/signin.go

@@ -0,0 +1,145 @@
+/*
+   GoToSocial
+   Copyright (C) 2021-2022 GoToSocial Authors admin@gotosocial.org
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Affero General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Affero General Public License for more details.
+
+   You should have received a copy of the GNU Affero General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+package auth
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net/http"
+
+	"github.com/gin-contrib/sessions"
+	"github.com/gin-gonic/gin"
+	apiutil "github.com/superseriousbusiness/gotosocial/internal/api/util"
+	"github.com/superseriousbusiness/gotosocial/internal/config"
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+	"github.com/superseriousbusiness/gotosocial/internal/oauth"
+	"golang.org/x/crypto/bcrypt"
+)
+
+// login just wraps a form-submitted username (we want an email) and password
+type login struct {
+	Email    string `form:"username"`
+	Password string `form:"password"`
+}
+
+// SignInGETHandler should be served at https://example.org/auth/sign_in.
+// The idea is to present a sign in page to the user, where they can enter their username and password.
+// The form will then POST to the sign in page, which will be handled by SignInPOSTHandler.
+// If an idp provider is set, then the user will be redirected to that to do their sign in.
+func (m *Module) SignInGETHandler(c *gin.Context) {
+	if _, err := apiutil.NegotiateAccept(c, apiutil.HTMLAcceptHeaders...); err != nil {
+		apiutil.ErrorHandler(c, gtserror.NewErrorNotAcceptable(err, err.Error()), m.processor.InstanceGet)
+		return
+	}
+
+	if !config.GetOIDCEnabled() {
+		instance, errWithCode := m.processor.InstanceGet(c.Request.Context(), config.GetHost())
+		if errWithCode != nil {
+			apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGet)
+			return
+		}
+
+		// no idp provider, use our own funky little sign in page
+		c.HTML(http.StatusOK, "sign-in.tmpl", gin.H{
+			"instance": instance,
+		})
+		return
+	}
+
+	// idp provider is in use, so redirect to it
+	s := sessions.Default(c)
+
+	internalStateI := s.Get(sessionInternalState)
+	internalState, ok := internalStateI.(string)
+	if !ok {
+		m.clearSession(s)
+		err := fmt.Errorf("key %s was not found in session", sessionInternalState)
+		apiutil.ErrorHandler(c, gtserror.NewErrorBadRequest(err, err.Error()), m.processor.InstanceGet)
+		return
+	}
+
+	c.Redirect(http.StatusSeeOther, m.idp.AuthCodeURL(internalState))
+}
+
+// SignInPOSTHandler should be served at https://example.org/auth/sign_in.
+// The idea is to present a sign in page to the user, where they can enter their username and password.
+// The handler will then redirect to the auth handler served at /auth
+func (m *Module) SignInPOSTHandler(c *gin.Context) {
+	s := sessions.Default(c)
+
+	form := &login{}
+	if err := c.ShouldBind(form); err != nil {
+		m.clearSession(s)
+		apiutil.ErrorHandler(c, gtserror.NewErrorBadRequest(err, oauth.HelpfulAdvice), m.processor.InstanceGet)
+		return
+	}
+
+	userid, errWithCode := m.ValidatePassword(c.Request.Context(), form.Email, form.Password)
+	if errWithCode != nil {
+		// don't clear session here, so the user can just press back and try again
+		// if they accidentally gave the wrong password or something
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGet)
+		return
+	}
+
+	s.Set(sessionUserID, userid)
+	if err := s.Save(); err != nil {
+		err := fmt.Errorf("error saving user id onto session: %s", err)
+		apiutil.ErrorHandler(c, gtserror.NewErrorInternalError(err, oauth.HelpfulAdvice), m.processor.InstanceGet)
+	}
+
+	c.Redirect(http.StatusFound, "/oauth"+OauthAuthorizePath)
+}
+
+// ValidatePassword takes an email address and a password.
+// The goal is to authenticate the password against the one for that email
+// address stored in the database. If OK, we return the userid (a ulid) for that user,
+// so that it can be used in further Oauth flows to generate a token/retreieve an oauth client from the db.
+func (m *Module) ValidatePassword(ctx context.Context, email string, password string) (string, gtserror.WithCode) {
+	if email == "" || password == "" {
+		err := errors.New("email or password was not provided")
+		return incorrectPassword(err)
+	}
+
+	user, err := m.db.GetUserByEmailAddress(ctx, email)
+	if err != nil {
+		err := fmt.Errorf("user %s was not retrievable from db during oauth authorization attempt: %s", email, err)
+		return incorrectPassword(err)
+	}
+
+	if user.EncryptedPassword == "" {
+		err := fmt.Errorf("encrypted password for user %s was empty for some reason", user.Email)
+		return incorrectPassword(err)
+	}
+
+	if err := bcrypt.CompareHashAndPassword([]byte(user.EncryptedPassword), []byte(password)); err != nil {
+		err := fmt.Errorf("password hash didn't match for user %s during login attempt: %s", user.Email, err)
+		return incorrectPassword(err)
+	}
+
+	return user.ID, nil
+}
+
+// incorrectPassword wraps the given error in a gtserror.WithCode, and returns
+// only a generic 'safe' error message to the user, to not give any info away.
+func incorrectPassword(err error) (string, gtserror.WithCode) {
+	safeErr := fmt.Errorf("password/email combination was incorrect")
+	return "", gtserror.NewErrorUnauthorized(err, safeErr.Error(), oauth.HelpfulAdvice)
+}