fix(login): ensure auth request (#8004)

# Which Problems Are Solved

Potential nil pointers leading to a panic in the login UI.

# How the Problems Are Solved

As of now the login UI did not always check if the authRequest was
actually retrieved form the database, which is ok for some endpoints
which can also be called outside of an auth request.
There are now methods added to ensure the request is loaded.

# Additional Changes

None

# Additional Context

Closes https://github.com/zitadel/DevOps/issues/55

internal/api/ui/login/auth_request.go

@@ -7,6 +7,7 @@ import (
 
 	http_mw "github.com/zitadel/zitadel/internal/api/http/middleware"
 	"github.com/zitadel/zitadel/internal/domain"
+	"github.com/zitadel/zitadel/internal/zerrors"
 )
 
 const (
@@ -23,6 +24,14 @@ func (l *Login) getAuthRequest(r *http.Request) (*domain.AuthRequest, error) {
 	return l.authRepo.AuthRequestByID(r.Context(), authRequestID, userAgentID)
 }
 
+func (l *Login) ensureAuthRequest(r *http.Request) (*domain.AuthRequest, error) {
+	authRequest, err := l.getAuthRequest(r)
+	if authRequest != nil || err != nil {
+		return authRequest, err
+	}
+	return nil, zerrors.ThrowInvalidArgument(nil, "LOGIN-OLah9", "invalid or missing auth request")
+}
+
 func (l *Login) getAuthRequestAndParseData(r *http.Request, data interface{}) (*domain.AuthRequest, error) {
 	authReq, err := l.getAuthRequest(r)
 	if err != nil {
@@ -32,6 +41,15 @@ func (l *Login) getAuthRequestAndParseData(r *http.Request, data interface{}) (*
 	return authReq, err
 }
 
+func (l *Login) ensureAuthRequestAndParseData(r *http.Request, data interface{}) (*domain.AuthRequest, error) {
+	authReq, err := l.ensureAuthRequest(r)
+	if err != nil {
+		return authReq, err
+	}
+	err = l.parser.Parse(r, data)
+	return authReq, err
+}
+
 func (l *Login) getParseData(r *http.Request, data interface{}) error {
 	return l.parser.Parse(r, data)
 }