feat(idp): provide option to auto link user (#7734)

* init auto linking

* prompt handling

* working

* translations

* console

* fixes

* unify

* custom texts

* fix tests

* linting

* fix check of existing user

* fix bg translation

* set unspecified as default in the form

internal/api/ui/login/link_prompt_handler.go

@@ -0,0 +1,62 @@
+package login
+
+import (
+	"net/http"
+
+	"github.com/zitadel/zitadel/internal/domain"
+	"github.com/zitadel/zitadel/internal/query"
+)
+
+const (
+	tmplLinkingUserPrompt = "link_user_prompt"
+)
+
+type linkingUserPromptData struct {
+	userData
+	Username string
+	Linking  domain.AutoLinkingOption
+	UserID   string
+}
+
+type linkingUserPromptFormData struct {
+	OtherUser bool   `schema:"other"`
+	UserID    string `schema:"userID"`
+}
+
+func (l *Login) renderLinkingUserPrompt(w http.ResponseWriter, r *http.Request, authReq *domain.AuthRequest, user *query.NotifyUser, err error) {
+	var errID, errMessage string
+	if err != nil {
+		errID, errMessage = l.getErrorMessage(r, err)
+	}
+	translator := l.getTranslator(r.Context(), authReq)
+	identification := user.PreferredLoginName
+	// hide the suffix in case the option is set and the auth request has been started with the primary domain scope
+	if authReq.RequestedOrgDomain && authReq.LabelPolicy != nil && authReq.LabelPolicy.HideLoginNameSuffix {
+		identification = user.Username
+	}
+	data := &linkingUserPromptData{
+		Username: identification,
+		UserID:   user.ID,
+		userData: l.getUserData(r, authReq, translator, "LinkingUserPrompt.Title", "LinkingUserPrompt.Description", errID, errMessage),
+	}
+	l.renderer.RenderTemplate(w, r, translator, l.renderer.Templates[tmplLinkingUserPrompt], data, nil)
+}
+
+func (l *Login) handleLinkingUserPrompt(w http.ResponseWriter, r *http.Request) {
+	data := new(linkingUserPromptFormData)
+	authReq, err := l.getAuthRequestAndParseData(r, data)
+	if err != nil {
+		l.renderLogin(w, r, authReq, err)
+		return
+	}
+	if data.OtherUser {
+		l.renderExternalNotFoundOption(w, r, authReq, nil, nil, nil, nil)
+		return
+	}
+	err = l.authRepo.SelectUser(r.Context(), authReq.ID, data.UserID, authReq.AgentID)
+	if err != nil {
+		l.renderLogin(w, r, authReq, err)
+		return
+	}
+	l.renderNextStep(w, r, authReq)
+}