sso: support public MCIAS authorize URL for non-Tailnet browsers

Add [sso].public_url: the browser-facing MCIAS base URL for the SSO
authorize redirect, kept separate from [mcias].server_url (the internal
address used for the server-to-server code exchange). Enables public SSO
without routing internal auth through the edge. Bumps mcdsl to v1.9.0.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

go.mod

@@ -4,7 +4,7 @@ go 1.25.7
 
 require (
 	git.wntrmute.dev/kyle/goutils v1.21.0
-	git.wntrmute.dev/mc/mcdsl v1.7.0
+	git.wntrmute.dev/mc/mcdsl v1.9.0
 	github.com/go-chi/chi/v5 v5.2.5
 	github.com/spf13/cobra v1.10.2
 	github.com/spf13/viper v1.21.0

go.sum

@@ -1,7 +1,7 @@
 git.wntrmute.dev/kyle/goutils v1.21.0 h1:ZR7ovV400hsF09zc8tkdHs6vyen8TDJ7flong/dnFXM=
 git.wntrmute.dev/kyle/goutils v1.21.0/go.mod h1:JQ8NL5lHSEYl719UMf20p4G1ei70RVGma0hjjNXCR2c=
-git.wntrmute.dev/mc/mcdsl v1.7.0 h1:dAh2SGdzjhz0H66i3KAMDm1eRYYgMaxqQ0Pj5NzF7fc=
+git.wntrmute.dev/mc/mcdsl v1.9.0 h1:TGqVhf9uhhh5jpMhN+8eNtBPSi/wwNXQn/NFDAcU4wg=
-git.wntrmute.dev/mc/mcdsl v1.7.0/go.mod h1:MhYahIu7Sg53lE2zpQ20nlrsoNRjQzOJBAlCmom2wJc=
+git.wntrmute.dev/mc/mcdsl v1.9.0/go.mod h1:MhYahIu7Sg53lE2zpQ20nlrsoNRjQzOJBAlCmom2wJc=
 github.com/cespare/xxhash/v2 v2.3.0 h1:UL815xU9SqsFlibzuggzjXhog7bL6oX9BbNZnL2UFvs=
 github.com/cespare/xxhash/v2 v2.3.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
 github.com/cpuguy83/go-md2man/v2 v2.0.6/go.mod h1:oOW0eioCTA6cOiMLiUPZOpcVxMig6NIQQ7OS05n1F4g=

internal/config/config.go

@@ -37,8 +37,16 @@ type MCIASConfig struct {
 // SSOConfig holds SSO redirect settings for the web UI.
 type SSOConfig struct {
 	// RedirectURI is the callback URL that MCIAS redirects to after login.
-	// Must exactly match the redirect_uri registered in MCIAS config.
+	// Must exactly match the redirect_uri registered in MCIAS config. For
+	// public (non-Tailnet) browser access this must be the public hostname.
 	RedirectURI string `toml:"redirect_uri"`
+
+	// PublicURL is the browser-facing MCIAS base URL used to build the SSO
+	// authorize redirect (e.g. "https://mcias.metacircular.net"). When empty,
+	// the backend [mcias].server_url is used for the redirect too. Set this
+	// when browsers cannot resolve the internal MCIAS name; the
+	// server-to-server code exchange still uses [mcias].server_url.
+	PublicURL string `toml:"public_url"`
 }
 
 // WebConfig holds settings for the standalone web UI server (metacrypt-web).

internal/webserver/server.go

@@ -175,6 +175,7 @@ func New(cfg *config.Config, logger *slog.Logger) (*WebServer, error) {
 	if cfg.SSO.RedirectURI != "" {
 		ssoClient, ssoErr := mcdsso.New(mcdsso.Config{
 			MciasURL:    cfg.MCIAS.ServerURL,
+			PublicURL:   cfg.SSO.PublicURL,
 			ClientID:    "metacrypt",
 			RedirectURI: cfg.SSO.RedirectURI,
 			CACert:      cfg.MCIAS.CACert,
@@ -183,7 +184,12 @@ func New(cfg *config.Config, logger *slog.Logger) (*WebServer, error) {
 			return nil, fmt.Errorf("webserver: create SSO client: %w", ssoErr)
 		}
 		ws.ssoClient = ssoClient
-		logger.Info("SSO enabled: redirecting to MCIAS for login", "mcias_url", cfg.MCIAS.ServerURL)
+		authorizeURL := cfg.SSO.PublicURL
+		if authorizeURL == "" {
+			authorizeURL = cfg.MCIAS.ServerURL
+		}
+		logger.Info("SSO enabled: redirecting to MCIAS for login",
+			"authorize_url", authorizeURL, "exchange_url", cfg.MCIAS.ServerURL)
 	}
 
 	if tok := cfg.MCIAS.ServiceToken; tok != "" {

vendor/git.wntrmute.dev/mc/mcdsl/db/db.go

@@ -65,11 +65,11 @@ func Open(path string) (*sql.DB, error) {
 	// connection to serialize all access and eliminate busy errors.
 	database.SetMaxOpenConns(1)
 
-	// Ensure permissions are correct even if the file already existed.
+	// Best-effort permissions tightening. This may fail inside rootless
-	if err := os.Chmod(path, 0600); err != nil {
+	// podman containers where fchmod is denied in the user namespace.
-		_ = database.Close()
+	// The database still functions correctly without it.
-		return nil, fmt.Errorf("db: chmod %s: %w", path, err)
+	// See: log/2026-04-03-uid-incident.md
-	}
+	_ = os.Chmod(path, 0600)
 
 	return database, nil
 }
@@ -168,9 +168,7 @@ func Snapshot(database *sql.DB, destPath string) error {
 		return fmt.Errorf("db: snapshot: %w", err)
 	}
 
-	if err := os.Chmod(destPath, 0600); err != nil {
+	_ = os.Chmod(destPath, 0600) // best-effort; may fail in rootless containers
-		return fmt.Errorf("db: chmod snapshot %s: %w", destPath, err)
-	}
 
 	return nil
 }

vendor/git.wntrmute.dev/mc/mcdsl/sso/sso.go

@@ -39,9 +39,18 @@ const (
 // Config holds the SSO client configuration. The values must match the
 // SSO client registration in MCIAS config.
 type Config struct {
-	// MciasURL is the base URL of the MCIAS server.
+	// MciasURL is the base URL of the MCIAS server used for the
+	// server-to-server authorization-code exchange. This is typically the
+	// internal/Tailnet address so the exchange does not depend on the public
+	// edge.
 	MciasURL string
 
+	// PublicURL, when set, is the browser-facing MCIAS base URL used to build
+	// the authorize redirect. It must be resolvable and reachable by end-user
+	// browsers (e.g. the public hostname). When empty, MciasURL is used for
+	// both, which only works when MciasURL is itself browser-reachable.
+	PublicURL string
+
 	// ClientID is the registered SSO client identifier.
 	ClientID string
 
@@ -104,9 +113,19 @@ func New(cfg Config) (*Client, error) {
 	}, nil
 }
 
-// AuthorizeURL returns the MCIAS authorize URL with the given state parameter.
+// authorizeBase returns the browser-facing MCIAS base URL: PublicURL when
+// configured, otherwise MciasURL.
+func (c *Client) authorizeBase() string {
+	if c.cfg.PublicURL != "" {
+		return c.cfg.PublicURL
+	}
+	return c.cfg.MciasURL
+}
+
+// AuthorizeURL returns the MCIAS authorize URL (browser-facing) with the
+// given state parameter.
 func (c *Client) AuthorizeURL(state string) string {
-	base := strings.TrimRight(c.cfg.MciasURL, "/")
+	base := strings.TrimRight(c.authorizeBase(), "/")
 	return base + "/sso/authorize?" + url.Values{
 		"client_id":    {c.cfg.ClientID},
 		"redirect_uri": {c.cfg.RedirectURI},

vendor/modules.txt

@@ -2,7 +2,7 @@
 ## explicit; go 1.24.0
 git.wntrmute.dev/kyle/goutils/certlib/certgen
 git.wntrmute.dev/kyle/goutils/lib
-# git.wntrmute.dev/mc/mcdsl v1.7.0
+# git.wntrmute.dev/mc/mcdsl v1.9.0
 ## explicit; go 1.25.7
 git.wntrmute.dev/mc/mcdsl/auth
 git.wntrmute.dev/mc/mcdsl/config