User password change (#280)

* start passwordChangeHandler

* add user scope

* add user module / api path

* add password change request

* make comment clearer

* add user to processor

* required true

* add processor call to handler

* don't pass tc or channel

* change password func + tests

* add some first docs about password management

* update swagger docs

* add api tests

* go fmt

* test fixes

11 files changed, 681 insertions, 0 deletions

diff --git a/internal/api/client/user/passwordchange.go b/internal/api/client/user/passwordchange.go
new file mode 100644
index 000000000..581abe526
--- /dev/null
+++ b/internal/api/client/user/passwordchange.go
@@ -0,0 +1,97 @@
+/*
+   GoToSocial
+   Copyright (C) 2021 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 user
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+	"github.com/sirupsen/logrus"
+	"github.com/superseriousbusiness/gotosocial/internal/api/model"
+	"github.com/superseriousbusiness/gotosocial/internal/oauth"
+)
+
+// PasswordChangePOSTHandler swagger:operation POST /api/v1/user/password_change userPasswordChange
+//
+// Change the password of authenticated user.
+//
+// The parameters can also be given in the body of the request, as JSON, if the content-type is set to 'application/json'.
+// The parameters can also be given in the body of the request, as XML, if the content-type is set to 'application/xml'.
+//
+// ---
+// tags:
+// - user
+//
+// consumes:
+// - application/json
+// - application/xml
+// - application/x-www-form-urlencoded
+//
+// produces:
+// - application/json
+//
+// security:
+// - OAuth2 Bearer:
+//   - write:user
+//
+// responses:
+//   '200':
+//     description: Change successful
+//   '401':
+//      description: unauthorized
+//   '403':
+//      description: forbidden
+//   '400':
+//      description: bad request
+//   '500':
+//      description: "internal error"
+func (m *Module) PasswordChangePOSTHandler(c *gin.Context) {
+	l := logrus.WithField("func", "PasswordChangePOSTHandler")
+
+	authed, err := oauth.Authed(c, true, true, true, true)
+	if err != nil {
+		l.Debugf("error authing: %s", err)
+		c.JSON(http.StatusUnauthorized, gin.H{"error": "unauthorized"})
+		return
+	}
+
+	// First check this user/account is active.
+	if authed.User.Disabled || !authed.User.Approved || !authed.Account.SuspendedAt.IsZero() {
+		l.Debugf("couldn't auth: %s", err)
+		c.JSON(http.StatusForbidden, gin.H{"error": "account is disabled, not yet approved, or suspended"})
+		return
+	}
+
+	form := &model.PasswordChangeRequest{}
+	if err := c.ShouldBind(form); err != nil || form == nil || form.NewPassword == "" || form.OldPassword == "" {
+		if err != nil {
+			l.Debugf("could not parse form from request: %s", err)
+		}
+		c.JSON(http.StatusBadRequest, gin.H{"error": "missing one or more required form values"})
+		return
+	}
+
+	if errWithCode := m.processor.UserChangePassword(c.Request.Context(), authed, form); errWithCode != nil {
+		l.Debugf("error changing user password: %s", errWithCode.Error())
+		c.JSON(errWithCode.Code(), gin.H{"error": errWithCode.Safe()})
+		return
+	}
+
+	c.Status(http.StatusOK)
+}
diff --git a/internal/api/client/user/passwordchange_test.go b/internal/api/client/user/passwordchange_test.go
new file mode 100644
index 000000000..bdbeb3e42
--- /dev/null
+++ b/internal/api/client/user/passwordchange_test.go
@@ -0,0 +1,157 @@
+/*
+   GoToSocial
+   Copyright (C) 2021 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 user_test
+
+import (
+	"context"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"testing"
+
+	"github.com/gin-gonic/gin"
+	"github.com/stretchr/testify/suite"
+	"github.com/superseriousbusiness/gotosocial/internal/api/client/user"
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+	"github.com/superseriousbusiness/gotosocial/internal/oauth"
+	"golang.org/x/crypto/bcrypt"
+)
+
+type PasswordChangeTestSuite struct {
+	UserStandardTestSuite
+}
+
+func (suite *PasswordChangeTestSuite) TestPasswordChangePOST() {
+	t := suite.testTokens["local_account_1"]
+	oauthToken := oauth.DBTokenToToken(t)
+
+	recorder := httptest.NewRecorder()
+	ctx, _ := gin.CreateTestContext(recorder)
+	ctx.Set(oauth.SessionAuthorizedApplication, suite.testApplications["application_1"])
+	ctx.Set(oauth.SessionAuthorizedToken, oauthToken)
+	ctx.Set(oauth.SessionAuthorizedUser, suite.testUsers["local_account_1"])
+	ctx.Set(oauth.SessionAuthorizedAccount, suite.testAccounts["local_account_1"])
+	ctx.Request = httptest.NewRequest(http.MethodPost, fmt.Sprintf("http://localhost:8080/%s", user.PasswordChangePath), nil)
+	ctx.Request.Form = url.Values{
+		"old_password": {"password"},
+		"new_password": {"peepeepoopoopassword"},
+	}
+	suite.userModule.PasswordChangePOSTHandler(ctx)
+
+	// check response
+	suite.EqualValues(http.StatusOK, recorder.Code)
+
+	dbUser := &gtsmodel.User{}
+	err := suite.db.GetByID(context.Background(), suite.testUsers["local_account_1"].ID, dbUser)
+	suite.NoError(err)
+
+	// new password should pass
+	err = bcrypt.CompareHashAndPassword([]byte(dbUser.EncryptedPassword), []byte("peepeepoopoopassword"))
+	suite.NoError(err)
+
+	// old password should fail
+	err = bcrypt.CompareHashAndPassword([]byte(dbUser.EncryptedPassword), []byte("password"))
+	suite.EqualError(err, "crypto/bcrypt: hashedPassword is not the hash of the given password")
+}
+
+func (suite *PasswordChangeTestSuite) TestPasswordMissingOldPassword() {
+	t := suite.testTokens["local_account_1"]
+	oauthToken := oauth.DBTokenToToken(t)
+
+	recorder := httptest.NewRecorder()
+	ctx, _ := gin.CreateTestContext(recorder)
+	ctx.Set(oauth.SessionAuthorizedApplication, suite.testApplications["application_1"])
+	ctx.Set(oauth.SessionAuthorizedToken, oauthToken)
+	ctx.Set(oauth.SessionAuthorizedUser, suite.testUsers["local_account_1"])
+	ctx.Set(oauth.SessionAuthorizedAccount, suite.testAccounts["local_account_1"])
+	ctx.Request = httptest.NewRequest(http.MethodPost, fmt.Sprintf("http://localhost:8080/%s", user.PasswordChangePath), nil)
+	ctx.Request.Form = url.Values{
+		"new_password": {"peepeepoopoopassword"},
+	}
+	suite.userModule.PasswordChangePOSTHandler(ctx)
+
+	// check response
+	suite.EqualValues(http.StatusBadRequest, recorder.Code)
+
+	result := recorder.Result()
+	defer result.Body.Close()
+	b, err := ioutil.ReadAll(result.Body)
+	suite.NoError(err)
+	suite.Equal(`{"error":"missing one or more required form values"}`, string(b))
+}
+
+func (suite *PasswordChangeTestSuite) TestPasswordIncorrectOldPassword() {
+	t := suite.testTokens["local_account_1"]
+	oauthToken := oauth.DBTokenToToken(t)
+
+	recorder := httptest.NewRecorder()
+	ctx, _ := gin.CreateTestContext(recorder)
+	ctx.Set(oauth.SessionAuthorizedApplication, suite.testApplications["application_1"])
+	ctx.Set(oauth.SessionAuthorizedToken, oauthToken)
+	ctx.Set(oauth.SessionAuthorizedUser, suite.testUsers["local_account_1"])
+	ctx.Set(oauth.SessionAuthorizedAccount, suite.testAccounts["local_account_1"])
+	ctx.Request = httptest.NewRequest(http.MethodPost, fmt.Sprintf("http://localhost:8080/%s", user.PasswordChangePath), nil)
+	ctx.Request.Form = url.Values{
+		"old_password": {"notright"},
+		"new_password": {"peepeepoopoopassword"},
+	}
+	suite.userModule.PasswordChangePOSTHandler(ctx)
+
+	// check response
+	suite.EqualValues(http.StatusBadRequest, recorder.Code)
+
+	result := recorder.Result()
+	defer result.Body.Close()
+	b, err := ioutil.ReadAll(result.Body)
+	suite.NoError(err)
+	suite.Equal(`{"error":"bad request: old password did not match"}`, string(b))
+}
+
+func (suite *PasswordChangeTestSuite) TestPasswordWeakNewPassword() {
+	t := suite.testTokens["local_account_1"]
+	oauthToken := oauth.DBTokenToToken(t)
+
+	recorder := httptest.NewRecorder()
+	ctx, _ := gin.CreateTestContext(recorder)
+	ctx.Set(oauth.SessionAuthorizedApplication, suite.testApplications["application_1"])
+	ctx.Set(oauth.SessionAuthorizedToken, oauthToken)
+	ctx.Set(oauth.SessionAuthorizedUser, suite.testUsers["local_account_1"])
+	ctx.Set(oauth.SessionAuthorizedAccount, suite.testAccounts["local_account_1"])
+	ctx.Request = httptest.NewRequest(http.MethodPost, fmt.Sprintf("http://localhost:8080/%s", user.PasswordChangePath), nil)
+	ctx.Request.Form = url.Values{
+		"old_password": {"password"},
+		"new_password": {"peepeepoopoo"},
+	}
+	suite.userModule.PasswordChangePOSTHandler(ctx)
+
+	// check response
+	suite.EqualValues(http.StatusBadRequest, recorder.Code)
+
+	result := recorder.Result()
+	defer result.Body.Close()
+	b, err := ioutil.ReadAll(result.Body)
+	suite.NoError(err)
+	suite.Equal(`{"error":"bad request: insecure password, try including more special characters, using uppercase letters, using numbers or using a longer password"}`, string(b))
+}
+
+func TestPasswordChangeTestSuite(t *testing.T) {
+	suite.Run(t, &PasswordChangeTestSuite{})
+}
diff --git a/internal/api/client/user/user.go b/internal/api/client/user/user.go
new file mode 100644
index 000000000..ff28a197f
--- /dev/null
+++ b/internal/api/client/user/user.go
@@ -0,0 +1,55 @@
+/*
+   GoToSocial
+   Copyright (C) 2021 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 user
+
+import (
+	"net/http"
+
+	"github.com/superseriousbusiness/gotosocial/internal/api"
+	"github.com/superseriousbusiness/gotosocial/internal/config"
+	"github.com/superseriousbusiness/gotosocial/internal/processing"
+	"github.com/superseriousbusiness/gotosocial/internal/router"
+)
+
+const (
+	// BasePath is the base URI path for this module
+	BasePath = "/api/v1/user"
+	// PasswordChangePath is the path for POSTing a password change request.
+	PasswordChangePath = BasePath + "/password_change"
+)
+
+// Module implements the ClientAPIModule interface
+type Module struct {
+	config    *config.Config
+	processor processing.Processor
+}
+
+// New returns a new user module
+func New(config *config.Config, processor processing.Processor) api.ClientModule {
+	return &Module{
+		config:    config,
+		processor: processor,
+	}
+}
+
+// Route attaches all routes from this module to the given router
+func (m *Module) Route(r router.Router) error {
+	r.AttachHandler(http.MethodPost, PasswordChangePath, m.PasswordChangePOSTHandler)
+	return nil
+}
diff --git a/internal/api/client/user/user_test.go b/internal/api/client/user/user_test.go
new file mode 100644
index 000000000..02f10b5ae
--- /dev/null
+++ b/internal/api/client/user/user_test.go
@@ -0,0 +1,73 @@
+/*
+   GoToSocial
+   Copyright (C) 2021 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 user_test
+
+import (
+	"git.iim.gay/grufwub/go-store/kv"
+	"github.com/stretchr/testify/suite"
+	"github.com/superseriousbusiness/gotosocial/internal/api/client/user"
+	"github.com/superseriousbusiness/gotosocial/internal/config"
+	"github.com/superseriousbusiness/gotosocial/internal/db"
+	"github.com/superseriousbusiness/gotosocial/internal/federation"
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+	"github.com/superseriousbusiness/gotosocial/internal/processing"
+	"github.com/superseriousbusiness/gotosocial/internal/typeutils"
+	"github.com/superseriousbusiness/gotosocial/testrig"
+)
+
+type UserStandardTestSuite struct {
+	suite.Suite
+	config    *config.Config
+	db        db.DB
+	tc        typeutils.TypeConverter
+	federator federation.Federator
+	processor processing.Processor
+	storage   *kv.KVStore
+
+	testTokens       map[string]*gtsmodel.Token
+	testClients      map[string]*gtsmodel.Client
+	testApplications map[string]*gtsmodel.Application
+	testUsers        map[string]*gtsmodel.User
+	testAccounts     map[string]*gtsmodel.Account
+
+	userModule *user.Module
+}
+
+func (suite *UserStandardTestSuite) SetupTest() {
+	suite.testTokens = testrig.NewTestTokens()
+	suite.testClients = testrig.NewTestClients()
+	suite.testApplications = testrig.NewTestApplications()
+	suite.testUsers = testrig.NewTestUsers()
+	suite.testAccounts = testrig.NewTestAccounts()
+	suite.config = testrig.NewTestConfig()
+	suite.db = testrig.NewTestDB()
+	suite.storage = testrig.NewTestStorage()
+	testrig.InitTestLog()
+	suite.tc = testrig.NewTestTypeConverter(suite.db)
+	suite.federator = testrig.NewTestFederator(suite.db, testrig.NewTestTransportController(testrig.NewMockHTTPClient(nil), suite.db), suite.storage)
+	suite.processor = testrig.NewTestProcessor(suite.db, suite.storage, suite.federator)
+	suite.userModule = user.New(suite.config, suite.processor).(*user.Module)
+	testrig.StandardDBSetup(suite.db, suite.testAccounts)
+	testrig.StandardStorageSetup(suite.storage, "../../../../testrig/media")
+}
+
+func (suite *UserStandardTestSuite) TearDownTest() {
+	testrig.StandardDBTeardown(suite.db)
+	testrig.StandardStorageTeardown(suite.storage)
+}
diff --git a/internal/api/model/user.go b/internal/api/model/user.go
new file mode 100644
index 000000000..3f639b5c3
--- /dev/null
+++ b/internal/api/model/user.go
@@ -0,0 +1,37 @@
+/*
+   GoToSocial
+   Copyright (C) 2021 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 model
+
+// PasswordChangeRequest models user password change parameters.
+//
+// swagger:parameters userPasswordChange
+type PasswordChangeRequest struct {
+	// User's previous password.
+	//
+	// in: formData
+	// required: true
+	OldPassword string `form:"old_password" json:"old_password" xml:"old_password" validation:"required"`
+	// Desired new password.
+	// If the password does not have high enough entropy, it will be rejected.
+	// See https://github.com/wagslane/go-password-validator
+	//
+	// in: formData
+	// required: true
+	NewPassword string `form:"new_password" json:"new_password" xml:"new_password" validation:"required"`
+}
diff --git a/internal/processing/processor.go b/internal/processing/processor.go
index 5732ad092..e61661dc9 100644
--- a/internal/processing/processor.go
+++ b/internal/processing/processor.go
@@ -39,6 +39,7 @@ import (
 	mediaProcessor "github.com/superseriousbusiness/gotosocial/internal/processing/media"
 	"github.com/superseriousbusiness/gotosocial/internal/processing/status"
 	"github.com/superseriousbusiness/gotosocial/internal/processing/streaming"
+	"github.com/superseriousbusiness/gotosocial/internal/processing/user"
 	"github.com/superseriousbusiness/gotosocial/internal/stream"
 	"github.com/superseriousbusiness/gotosocial/internal/timeline"
 	"github.com/superseriousbusiness/gotosocial/internal/typeutils"
@@ -173,6 +174,9 @@ type Processor interface {
 	// OpenStreamForAccount opens a new stream for the given account, with the given stream type.
 	OpenStreamForAccount(ctx context.Context, account *gtsmodel.Account, streamType string) (*stream.Stream, gtserror.WithCode)
 
+	// UserChangePassword changes the password for the given user, with the given form.
+	UserChangePassword(ctx context.Context, authed *oauth.Auth, form *apimodel.PasswordChangeRequest) gtserror.WithCode
+
 	/*
 		FEDERATION API-FACING PROCESSING FUNCTIONS
 		These functions are intended to be called when the federating client needs an immediate (ie., synchronous) reply
@@ -247,6 +251,7 @@ type processor struct {
 	statusProcessor    status.Processor
 	streamingProcessor streaming.Processor
 	mediaProcessor     mediaProcessor.Processor
+	userProcessor      user.Processor
 }
 
 // NewProcessor returns a new Processor that uses the given federator
@@ -259,6 +264,7 @@ func NewProcessor(config *config.Config, tc typeutils.TypeConverter, federator f
 	accountProcessor := account.New(db, tc, mediaHandler, oauthServer, fromClientAPI, federator, config)
 	adminProcessor := admin.New(db, tc, mediaHandler, fromClientAPI, config)
 	mediaProcessor := mediaProcessor.New(db, tc, mediaHandler, storage, config)
+	userProcessor := user.New(db, config)
 
 	return &processor{
 		fromClientAPI:   fromClientAPI,
@@ -279,6 +285,7 @@ func NewProcessor(config *config.Config, tc typeutils.TypeConverter, federator f
 		statusProcessor:    statusProcessor,
 		streamingProcessor: streamingProcessor,
 		mediaProcessor:     mediaProcessor,
+		userProcessor:      userProcessor,
 	}
 }
 
diff --git a/internal/processing/user.go b/internal/processing/user.go
new file mode 100644
index 000000000..a5fca53dd
--- /dev/null
+++ b/internal/processing/user.go
@@ -0,0 +1,31 @@
+/*
+   GoToSocial
+   Copyright (C) 2021 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 processing
+
+import (
+	"context"
+
+	apimodel "github.com/superseriousbusiness/gotosocial/internal/api/model"
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+	"github.com/superseriousbusiness/gotosocial/internal/oauth"
+)
+
+func (p *processor) UserChangePassword(ctx context.Context, authed *oauth.Auth, form *apimodel.PasswordChangeRequest) gtserror.WithCode {
+	return p.userProcessor.ChangePassword(ctx, authed.User, form.OldPassword, form.NewPassword)
+}
diff --git a/internal/processing/user/changepassword.go b/internal/processing/user/changepassword.go
new file mode 100644
index 000000000..3fe2c8d7c
--- /dev/null
+++ b/internal/processing/user/changepassword.go
@@ -0,0 +1,50 @@
+/*
+   GoToSocial
+   Copyright (C) 2021 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 user
+
+import (
+	"context"
+
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+	"github.com/superseriousbusiness/gotosocial/internal/validate"
+	"golang.org/x/crypto/bcrypt"
+)
+
+func (p *processor) ChangePassword(ctx context.Context, user *gtsmodel.User, oldPassword string, newPassword string) gtserror.WithCode {
+	if err := bcrypt.CompareHashAndPassword([]byte(user.EncryptedPassword), []byte(oldPassword)); err != nil {
+		return gtserror.NewErrorBadRequest(err, "old password did not match")
+	}
+
+	if err := validate.NewPassword(newPassword); err != nil {
+		return gtserror.NewErrorBadRequest(err, err.Error())
+	}
+
+	newPasswordHash, err := bcrypt.GenerateFromPassword([]byte(newPassword), bcrypt.DefaultCost)
+	if err != nil {
+		return gtserror.NewErrorInternalError(err, "error hashing password")
+	}
+
+	user.EncryptedPassword = string(newPasswordHash)
+	if err := p.db.UpdateByPrimaryKey(ctx, user); err != nil {
+		return gtserror.NewErrorInternalError(err, "database error")
+	}
+
+	return nil
+}
diff --git a/internal/processing/user/changepassword_test.go b/internal/processing/user/changepassword_test.go
new file mode 100644
index 000000000..2687eae10
--- /dev/null
+++ b/internal/processing/user/changepassword_test.go
@@ -0,0 +1,74 @@
+/*
+   GoToSocial
+   Copyright (C) 2021 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 user_test
+
+import (
+	"context"
+	"net/http"
+	"testing"
+
+	"github.com/stretchr/testify/suite"
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+	"golang.org/x/crypto/bcrypt"
+)
+
+type ChangePasswordTestSuite struct {
+	UserStandardTestSuite
+}
+
+func (suite *ChangePasswordTestSuite) TestChangePasswordOK() {
+	user := suite.testUsers["local_account_1"]
+
+	errWithCode := suite.user.ChangePassword(context.Background(), user, "password", "verygoodnewpassword")
+	suite.NoError(errWithCode)
+
+	err := bcrypt.CompareHashAndPassword([]byte(user.EncryptedPassword), []byte("verygoodnewpassword"))
+	suite.NoError(err)
+
+	// get user from the db again
+	dbUser := &gtsmodel.User{}
+	err = suite.db.GetByID(context.Background(), user.ID, dbUser)
+	suite.NoError(err)
+
+	// check the password has changed
+	err = bcrypt.CompareHashAndPassword([]byte(dbUser.EncryptedPassword), []byte("verygoodnewpassword"))
+	suite.NoError(err)
+}
+
+func (suite *ChangePasswordTestSuite) TestChangePasswordIncorrectOld() {
+	user := suite.testUsers["local_account_1"]
+
+	errWithCode := suite.user.ChangePassword(context.Background(), user, "ooooopsydoooopsy", "verygoodnewpassword")
+	suite.EqualError(errWithCode, "crypto/bcrypt: hashedPassword is not the hash of the given password")
+	suite.Equal(http.StatusBadRequest, errWithCode.Code())
+	suite.Equal("bad request: old password did not match", errWithCode.Safe())
+}
+
+func (suite *ChangePasswordTestSuite) TestChangePasswordWeakNew() {
+	user := suite.testUsers["local_account_1"]
+
+	errWithCode := suite.user.ChangePassword(context.Background(), user, "password", "1234")
+	suite.EqualError(errWithCode, "insecure password, try including more special characters, using lowercase letters, using uppercase letters or using a longer password")
+	suite.Equal(http.StatusBadRequest, errWithCode.Code())
+	suite.Equal("bad request: insecure password, try including more special characters, using lowercase letters, using uppercase letters or using a longer password", errWithCode.Safe())
+}
+
+func TestChangePasswordTestSuite(t *testing.T) {
+	suite.Run(t, &ChangePasswordTestSuite{})
+}
diff --git a/internal/processing/user/user.go b/internal/processing/user/user.go
new file mode 100644
index 000000000..c572becc2
--- /dev/null
+++ b/internal/processing/user/user.go
@@ -0,0 +1,48 @@
+/*
+   GoToSocial
+   Copyright (C) 2021 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 user
+
+import (
+	"context"
+
+	"github.com/superseriousbusiness/gotosocial/internal/config"
+	"github.com/superseriousbusiness/gotosocial/internal/db"
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+)
+
+// Processor wraps a bunch of functions for processing user-level actions.
+type Processor interface {
+	// ChangePassword changes the specified user's password from old => new,
+	// or returns an error if the new password is too weak, or the old password is incorrect.
+	ChangePassword(ctx context.Context, user *gtsmodel.User, oldPassword string, newPassword string) gtserror.WithCode
+}
+
+type processor struct {
+	config *config.Config
+	db     db.DB
+}
+
+// New returns a new user processor
+func New(db db.DB, config *config.Config) Processor {
+	return &processor{
+		config: config,
+		db:     db,
+	}
+}
diff --git a/internal/processing/user/user_test.go b/internal/processing/user/user_test.go
new file mode 100644
index 000000000..4f18e03c2
--- /dev/null
+++ b/internal/processing/user/user_test.go
@@ -0,0 +1,52 @@
+/*
+   GoToSocial
+   Copyright (C) 2021 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 user_test
+
+import (
+	"github.com/stretchr/testify/suite"
+	"github.com/superseriousbusiness/gotosocial/internal/config"
+	"github.com/superseriousbusiness/gotosocial/internal/db"
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+	"github.com/superseriousbusiness/gotosocial/internal/processing/user"
+	"github.com/superseriousbusiness/gotosocial/testrig"
+)
+
+type UserStandardTestSuite struct {
+	suite.Suite
+	config *config.Config
+	db     db.DB
+
+	testUsers map[string]*gtsmodel.User
+
+	user user.Processor
+}
+
+func (suite *UserStandardTestSuite) SetupTest() {
+	testrig.InitTestLog()
+	suite.config = testrig.NewTestConfig()
+	suite.db = testrig.NewTestDB()
+	suite.testUsers = testrig.NewTestUsers()
+	suite.user = user.New(suite.db, suite.config)
+
+	testrig.StandardDBSetup(suite.db, nil)
+}
+
+func (suite *UserStandardTestSuite) TearDownTest() {
+	testrig.StandardDBTeardown(suite.db)
+}