6 files changed, 35 insertions, 20 deletions
diff --git a/internal/api/client/auth/auth.go b/internal/api/client/auth/auth.go
index a097f8004..b12b6d24f 100644
--- a/internal/api/client/auth/auth.go
+++ b/internal/api/client/auth/auth.go
@@ -55,13 +55,14 @@ const (
 	callbackStateParam = "state"
 	callbackCodeParam  = "code"
 
-	sessionUserID       = "userid"
-	sessionClientID     = "client_id"
-	sessionRedirectURI  = "redirect_uri"
-	sessionForceLogin   = "force_login"
-	sessionResponseType = "response_type"
-	sessionScope        = "scope"
-	sessionState        = "state"
+	sessionUserID        = "userid"
+	sessionClientID      = "client_id"
+	sessionRedirectURI   = "redirect_uri"
+	sessionForceLogin    = "force_login"
+	sessionResponseType  = "response_type"
+	sessionScope         = "scope"
+	sessionInternalState = "internal_state"
+	sessionClientState   = "client_state"
 )
 
 // Module implements the ClientAPIModule interface for
diff --git a/internal/api/client/auth/authorize.go b/internal/api/client/auth/authorize.go
index 233dacfd2..1a594a319 100644
--- a/internal/api/client/auth/authorize.go
+++ b/internal/api/client/auth/authorize.go
@@ -189,6 +189,11 @@ func (m *Module) AuthorizePOSTHandler(c *gin.Context) {
 		errs = append(errs, fmt.Sprintf("key %s was not found in session", sessionScope))
 	}
 
+	var clientState string
+	if s, ok := s.Get(sessionClientState).(string); ok {
+		clientState = s
+	}
+
 	userID, ok := s.Get(sessionUserID).(string)
 	if !ok {
 		errs = append(errs, fmt.Sprintf("key %s was not found in session", sessionUserID))
@@ -246,6 +251,10 @@ func (m *Module) AuthorizePOSTHandler(c *gin.Context) {
 		sessionUserID:       {userID},
 	}
 
+	if clientState != "" {
+		c.Request.Form.Set("state", clientState)
+	}
+
 	if err := m.processor.OAuthHandleAuthorizeRequest(c.Writer, c.Request); err != nil {
 		api.ErrorHandler(c, gtserror.NewErrorBadRequest(err, err.Error(), helpfulAdvice), m.processor.InstanceGet)
 	}
@@ -285,7 +294,8 @@ func saveAuthFormToSession(s sessions.Session, form *model.OAuthAuthorize) gtser
 	s.Set(sessionClientID, form.ClientID)
 	s.Set(sessionRedirectURI, form.RedirectURI)
 	s.Set(sessionScope, form.Scope)
-	s.Set(sessionState, uuid.NewString())
+	s.Set(sessionInternalState, uuid.NewString())
+	s.Set(sessionClientState, form.State)
 
 	if err := s.Save(); err != nil {
 		err := fmt.Errorf("error saving form values onto session: %s", err)
diff --git a/internal/api/client/auth/callback.go b/internal/api/client/auth/callback.go
index 34a4995c8..96a73a52f 100644
--- a/internal/api/client/auth/callback.go
+++ b/internal/api/client/auth/callback.go
@@ -45,26 +45,26 @@ func (m *Module) CallbackGETHandler(c *gin.Context) {
 	// check the query vs session state parameter to mitigate csrf
 	// https://auth0.com/docs/secure/attack-protection/state-parameters
 
-	state := c.Query(callbackStateParam)
-	if state == "" {
+	returnedInternalState := c.Query(callbackStateParam)
+	if returnedInternalState == "" {
 		m.clearSession(s)
 		err := fmt.Errorf("%s parameter not found on callback query", callbackStateParam)
 		api.ErrorHandler(c, gtserror.NewErrorBadRequest(err, err.Error()), m.processor.InstanceGet)
 		return
 	}
 
-	savedStateI := s.Get(sessionState)
-	savedState, ok := savedStateI.(string)
+	savedInternalStateI := s.Get(sessionInternalState)
+	savedInternalState, ok := savedInternalStateI.(string)
 	if !ok {
 		m.clearSession(s)
-		err := fmt.Errorf("key %s was not found in session", sessionState)
+		err := fmt.Errorf("key %s was not found in session", sessionInternalState)
 		api.ErrorHandler(c, gtserror.NewErrorBadRequest(err, err.Error()), m.processor.InstanceGet)
 		return
 	}
 
-	if state != savedState {
+	if returnedInternalState != savedInternalState {
 		m.clearSession(s)
-		err := errors.New("mismatch between query state and session state")
+		err := errors.New("mismatch between callback state and saved state")
 		api.ErrorHandler(c, gtserror.NewErrorUnauthorized(err, err.Error()), m.processor.InstanceGet)
 		return
 	}
diff --git a/internal/api/client/auth/signin.go b/internal/api/client/auth/signin.go
index b8f267f54..f9541d4c5 100644
--- a/internal/api/client/auth/signin.go
+++ b/internal/api/client/auth/signin.go
@@ -58,16 +58,16 @@ func (m *Module) SignInGETHandler(c *gin.Context) {
 	// idp provider is in use, so redirect to it
 	s := sessions.Default(c)
 
-	stateI := s.Get(sessionState)
-	state, ok := stateI.(string)
+	internalStateI := s.Get(sessionInternalState)
+	internalState, ok := internalStateI.(string)
 	if !ok {
 		m.clearSession(s)
-		err := fmt.Errorf("key %s was not found in session", sessionState)
+		err := fmt.Errorf("key %s was not found in session", sessionInternalState)
 		api.ErrorHandler(c, gtserror.NewErrorBadRequest(err, err.Error()), m.processor.InstanceGet)
 		return
 	}
 
-	c.Redirect(http.StatusSeeOther, m.idp.AuthCodeURL(state))
+	c.Redirect(http.StatusSeeOther, m.idp.AuthCodeURL(internalState))
 }
 
 // SignInPOSTHandler should be served at https://example.org/auth/sign_in.
diff --git a/internal/api/client/status/statuscreate_test.go b/internal/api/client/status/statuscreate_test.go
index 2a1516d9b..93fe74175 100644
--- a/internal/api/client/status/statuscreate_test.go
+++ b/internal/api/client/status/statuscreate_test.go
@@ -312,7 +312,7 @@ func (suite *StatusCreateTestSuite) TestAttachNewMediaSuccess() {
 	ctx.Request = httptest.NewRequest(http.MethodPost, fmt.Sprintf("http://localhost:8080/%s", status.BasePath), nil) // the endpoint we're hitting
 	ctx.Request.Header.Set("accept", "application/json")
 	ctx.Request.Form = url.Values{
-		"status":    {"here's an image attachment"},
+		"status":      {"here's an image attachment"},
 		"media_ids[]": {attachment.ID},
 	}
 	suite.statusModule.StatusCreatePOSTHandler(ctx)
diff --git a/internal/api/model/oauth.go b/internal/api/model/oauth.go
index c86e4723e..e6dc0d42c 100644
--- a/internal/api/model/oauth.go
+++ b/internal/api/model/oauth.go
@@ -33,4 +33,8 @@ type OAuthAuthorize struct {
 	// List of requested OAuth scopes, separated by spaces (or by pluses, if using query parameters).
 	// Must be a subset of scopes declared during app registration. If not provided, defaults to read.
 	Scope string `form:"scope" json:"scope"`
+	// State is used by the application to store request-specific data and/or prevent CSRF attacks.
+	// The authorization server must return the unmodified state value back to the application.
+	// See https://www.oauth.com/oauth2-servers/authorization/the-authorization-request/
+	State string `form:"state" json:"state"`
 }