fix double login URL with OIDC (#2445)

* factor out login url parser

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

* move to not trigger test gen checker

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

* return regresp or err after waiting for registration

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

* update changelog

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

---------

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

hscontrol/util/util.go

@@ -1,6 +1,13 @@
 package util
 
-import "tailscale.com/util/cmpver"
+import (
+	"errors"
+	"fmt"
+	"net/url"
+	"strings"
+
+	"tailscale.com/util/cmpver"
+)
 
 func TailscaleVersionNewerOrEqual(minimum, toCheck string) bool {
 	if cmpver.Compare(minimum, toCheck) <= 0 ||
@@ -11,3 +18,31 @@ func TailscaleVersionNewerOrEqual(minimum, toCheck string) bool {
 
 	return false
 }
+
+// ParseLoginURLFromCLILogin parses the output of the tailscale up command to extract the login URL.
+// It returns an error if not exactly one URL is found.
+func ParseLoginURLFromCLILogin(output string) (*url.URL, error) {
+	lines := strings.Split(output, "\n")
+	var urlStr string
+
+	for _, line := range lines {
+		line = strings.TrimSpace(line)
+		if strings.HasPrefix(line, "http://") || strings.HasPrefix(line, "https://") {
+			if urlStr != "" {
+				return nil, fmt.Errorf("multiple URLs found: %s and %s", urlStr, line)
+			}
+			urlStr = line
+		}
+	}
+
+	if urlStr == "" {
+		return nil, errors.New("no URL found")
+	}
+
+	loginURL, err := url.Parse(urlStr)
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse URL: %w", err)
+	}
+
+	return loginURL, nil
+}