Fix SSO return-to redirect loop

SetReturnToCookie stored /sso/redirect as the return-to path,
causing a redirect loop after successful SSO login: the callback
would redirect back to /sso/redirect instead of /. Filter all
/sso/* paths, not just /sso/callback.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ARCHITECTURE.md

@@ -27,7 +27,7 @@ problem, usable independently or together.
 ### Module Path
 
 ```
-git.wntrmute.dev/kyle/mcdsl
+git.wntrmute.dev/mc/mcdsl
 ```
 
 ### Dependencies
@@ -39,7 +39,7 @@ git.wntrmute.dev/kyle/mcdsl
 | `github.com/pelletier/go-toml/v2` | TOML config parsing |
 | `google.golang.org/grpc` | gRPC server |
 | `github.com/klauspost/compress/zstd` | Zstandard compression for archives |
-| `git.wntrmute.dev/kyle/mcias/clients/go` | MCIAS client library |
+| `git.wntrmute.dev/mc/mcias/clients/go` | MCIAS client library |
 
 All dependencies are already used by existing services. MCDSL adds no new
 dependencies to the platform.

CLAUDE.md

@@ -6,7 +6,7 @@ This file provides guidance to Claude Code (claude.ai/code) when working with co
 
 MCDSL (Metacircular Dynamics Standard Library) is the shared Go library for the Metacircular platform. It extracts common patterns from production services into reusable, tested packages. MCDSL is not a deployed service — it is imported by other services.
 
-**Module path:** `git.wntrmute.dev/kyle/mcdsl`
+**Module path:** `git.wntrmute.dev/mc/mcdsl`
 
 ## Build Commands
 
@@ -37,6 +37,7 @@ go test ./auth/ -run TestCacheExpiry
 | `web` | Session cookies, auth middleware, template rendering for htmx UIs |
 | `health` | REST and gRPC health check handlers |
 | `archive` | tar.zst snapshots with SQLite-aware backup (VACUUM INTO) |
+| `terminal` | Secure terminal input (echo-suppressed password prompts) |
 
 ## Import Pattern
 
@@ -44,11 +45,11 @@ Services import individual packages with aliased imports:
 
 ```go
 import (
-    mcdslauth   "git.wntrmute.dev/kyle/mcdsl/auth"
+    mcdslauth   "git.wntrmute.dev/mc/mcdsl/auth"
-    mcdsldb     "git.wntrmute.dev/kyle/mcdsl/db"
+    mcdsldb     "git.wntrmute.dev/mc/mcdsl/db"
-    mcdslconfig "git.wntrmute.dev/kyle/mcdsl/config"
+    mcdslconfig "git.wntrmute.dev/mc/mcdsl/config"
-    "git.wntrmute.dev/kyle/mcdsl/httpserver"
+    "git.wntrmute.dev/mc/mcdsl/httpserver"
-    "git.wntrmute.dev/kyle/mcdsl/grpcserver"
+    "git.wntrmute.dev/mc/mcdsl/grpcserver"
 )
 ```
 
@@ -63,6 +64,7 @@ db --> (modernc.org/sqlite)
 grpcserver --> auth, config
 health --> db
 httpserver --> config
+terminal --> (golang.org/x/term)
 web --> auth, csrf
 ```
 

PROGRESS.md

@@ -91,11 +91,11 @@ Remaining mcat-specific code:
 - `web/` — templates and static assets (unchanged)
 
 Dependencies removed:
-- `git.wntrmute.dev/kyle/mcias/clients/go` (mcdsl/auth handles MCIAS directly)
+- `git.wntrmute.dev/mc/mcias/clients/go` (mcdsl/auth handles MCIAS directly)
 - `github.com/pelletier/go-toml/v2` (now indirect via mcdsl/config)
 
 Dependencies added:
-- `git.wntrmute.dev/kyle/mcdsl` (local replace directive)
+- `git.wntrmute.dev/mc/mcdsl` (local replace directive)
 
 Result: vet clean, lint 0 issues, builds successfully.
 

PROJECT_PLAN.md

@@ -10,7 +10,7 @@ code first).
 
 ## Phase 0: Project Setup
 
-- [ ] Initialize Go module (`git.wntrmute.dev/kyle/mcdsl`)
+- [ ] Initialize Go module (`git.wntrmute.dev/mc/mcdsl`)
 - [ ] Create `.golangci.yaml` (matching platform standard)
 - [ ] Create `Makefile` with standard targets (build, test, vet, lint, all)
 - [ ] Create `.gitignore`

README.md

@@ -25,7 +25,7 @@ it and provide only their service-specific logic.
 ## Module Path
 
 ```
-git.wntrmute.dev/kyle/mcdsl
+git.wntrmute.dev/mc/mcdsl
 ```
 
 ## Packages
@@ -46,10 +46,10 @@ git.wntrmute.dev/kyle/mcdsl
 
 ```go
 import (
-    "git.wntrmute.dev/kyle/mcdsl/auth"
+    "git.wntrmute.dev/mc/mcdsl/auth"
-    "git.wntrmute.dev/kyle/mcdsl/db"
+    "git.wntrmute.dev/mc/mcdsl/db"
-    "git.wntrmute.dev/kyle/mcdsl/config"
+    "git.wntrmute.dev/mc/mcdsl/config"
-    "git.wntrmute.dev/kyle/mcdsl/httpserver"
+    "git.wntrmute.dev/mc/mcdsl/httpserver"
 )
 
 // Load config with standard sections + service-specific fields.

archive/archive.go

@@ -20,7 +20,7 @@ import (
 
 	"github.com/klauspost/compress/zstd"
 
-	"git.wntrmute.dev/kyle/mcdsl/db"
+	"git.wntrmute.dev/mc/mcdsl/db"
 )
 
 // defaultExcludePatterns are always excluded from snapshots.

archive/archive_test.go

@@ -7,7 +7,7 @@ import (
 	"path/filepath"
 	"testing"
 
-	"git.wntrmute.dev/kyle/mcdsl/db"
+	"git.wntrmute.dev/mc/mcdsl/db"
 )
 
 // setupServiceDir creates a realistic /srv/<service>/ directory.

config/config.go

@@ -34,7 +34,7 @@ import (
 
 	"github.com/pelletier/go-toml/v2"
 
-	"git.wntrmute.dev/kyle/mcdsl/auth"
+	"git.wntrmute.dev/mc/mcdsl/auth"
 )
 
 // Base contains the configuration sections common to all Metacircular

go.mod

@@ -1,4 +1,4 @@
-module git.wntrmute.dev/kyle/mcdsl
+module git.wntrmute.dev/mc/mcdsl
 
 go 1.25.7
 
@@ -18,6 +18,7 @@ require (
 	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
 	golang.org/x/net v0.48.0 // indirect
 	golang.org/x/sys v0.42.0 // indirect
+	golang.org/x/term v0.41.0 // indirect
 	golang.org/x/text v0.32.0 // indirect
 	google.golang.org/genproto/googleapis/rpc v0.0.0-20251202230838-ff82c1b0f217 // indirect
 	google.golang.org/protobuf v1.36.10 // indirect

go.sum

@@ -49,6 +49,8 @@ golang.org/x/sync v0.19.0/go.mod h1:9KTHXmSnoGruLpwFjVSX0lNNA75CykiMECbovNTZqGI=
 golang.org/x/sys v0.6.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.42.0 h1:omrd2nAlyT5ESRdCLYdm3+fMfNFE/+Rf4bDIQImRJeo=
 golang.org/x/sys v0.42.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
+golang.org/x/term v0.41.0 h1:QCgPso/Q3RTJx2Th4bDLqML4W6iJiaXFq2/ftQF13YU=
+golang.org/x/term v0.41.0/go.mod h1:3pfBgksrReYfZ5lvYM0kSO0LIkAl4Yl2bXOkKP7Ec2A=
 golang.org/x/text v0.32.0 h1:ZD01bjUt1FQ9WJ0ClOL5vxgxOI/sVCNgX1YtKwcY0mU=
 golang.org/x/text v0.32.0/go.mod h1:o/rUWzghvpD5TXrTIBuJU77MTaN0ljMWE47kxGJQ7jY=
 golang.org/x/tools v0.42.0 h1:uNgphsn75Tdz5Ji2q36v/nsFSfR/9BRFvqhGBaJGd5k=

grpcserver/server.go

@@ -21,7 +21,7 @@ import (
 	"google.golang.org/grpc/metadata"
 	"google.golang.org/grpc/status"
 
-	"git.wntrmute.dev/kyle/mcdsl/auth"
+	"git.wntrmute.dev/mc/mcdsl/auth"
 )
 
 // MethodMap classifies gRPC methods for access control.

grpcserver/server_test.go

@@ -13,7 +13,7 @@ import (
 	"google.golang.org/grpc/metadata"
 	"google.golang.org/grpc/status"
 
-	"git.wntrmute.dev/kyle/mcdsl/auth"
+	"git.wntrmute.dev/mc/mcdsl/auth"
 )
 
 func mockMCIAS(t *testing.T) *httptest.Server {

health/health_test.go

@@ -10,7 +10,7 @@ import (
 
 	"google.golang.org/grpc"
 
-	"git.wntrmute.dev/kyle/mcdsl/db"
+	"git.wntrmute.dev/mc/mcdsl/db"
 )
 
 func TestHandlerHealthy(t *testing.T) {

httpserver/server.go

@@ -13,7 +13,7 @@ import (
 
 	"github.com/go-chi/chi/v5"
 
-	"git.wntrmute.dev/kyle/mcdsl/config"
+	"git.wntrmute.dev/mc/mcdsl/config"
 )
 
 // Server wraps a chi router and an http.Server with the standard

httpserver/server_test.go

@@ -9,7 +9,7 @@ import (
 	"testing"
 	"time"
 
-	"git.wntrmute.dev/kyle/mcdsl/config"
+	"git.wntrmute.dev/mc/mcdsl/config"
 )
 
 func testConfig() config.ServerConfig {

sso/sso.go

@@ -0,0 +1,304 @@
+// Package sso provides an SSO redirect client for Metacircular web services.
+//
+// Services redirect unauthenticated users to MCIAS for login. After
+// authentication, MCIAS redirects back with an authorization code that
+// the service exchanges for a JWT token. This package handles the
+// redirect, state management, and code exchange.
+//
+// Security design:
+//   - State cookies use SameSite=Lax (not Strict) because the redirect from
+//     MCIAS back to the service is a cross-site navigation.
+//   - State is a 256-bit random value stored in an HttpOnly cookie.
+//   - Return-to URLs are stored in a separate cookie so MCIAS never sees them.
+//   - The code exchange is a server-to-server HTTPS call (TLS 1.3 minimum).
+package sso
+
+import (
+	"bytes"
+	"context"
+	"crypto/rand"
+	"crypto/tls"
+	"crypto/x509"
+	"encoding/hex"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"os"
+	"strings"
+	"time"
+)
+
+const (
+	stateBytes     = 32     // 256 bits
+	stateCookieAge = 5 * 60 // 5 minutes in seconds
+)
+
+// 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 string
+
+	// ClientID is the registered SSO client identifier.
+	ClientID string
+
+	// RedirectURI is the callback URL that MCIAS redirects to after login.
+	// Must exactly match the redirect_uri registered in MCIAS config.
+	RedirectURI string
+
+	// CACert is an optional path to a PEM-encoded CA certificate for
+	// verifying the MCIAS server's TLS certificate.
+	CACert string
+}
+
+// Client handles the SSO redirect flow with MCIAS.
+type Client struct {
+	cfg        Config
+	httpClient *http.Client
+}
+
+// New creates an SSO client. TLS 1.3 is required for all HTTPS
+// connections to MCIAS.
+func New(cfg Config) (*Client, error) {
+	if cfg.MciasURL == "" {
+		return nil, fmt.Errorf("sso: mcias_url is required")
+	}
+	if cfg.ClientID == "" {
+		return nil, fmt.Errorf("sso: client_id is required")
+	}
+	if cfg.RedirectURI == "" {
+		return nil, fmt.Errorf("sso: redirect_uri is required")
+	}
+
+	transport := &http.Transport{}
+
+	if !strings.HasPrefix(cfg.MciasURL, "http://") {
+		tlsCfg := &tls.Config{
+			MinVersion: tls.VersionTLS13,
+		}
+
+		if cfg.CACert != "" {
+			pem, err := os.ReadFile(cfg.CACert) //nolint:gosec // CA cert path from operator config
+			if err != nil {
+				return nil, fmt.Errorf("sso: read CA cert %s: %w", cfg.CACert, err)
+			}
+			pool := x509.NewCertPool()
+			if !pool.AppendCertsFromPEM(pem) {
+				return nil, fmt.Errorf("sso: no valid certificates in %s", cfg.CACert)
+			}
+			tlsCfg.RootCAs = pool
+		}
+
+		transport.TLSClientConfig = tlsCfg
+	}
+
+	return &Client{
+		cfg: cfg,
+		httpClient: &http.Client{
+			Transport: transport,
+			Timeout:   10 * time.Second,
+		},
+	}, nil
+}
+
+// AuthorizeURL returns the MCIAS authorize URL with the given state parameter.
+func (c *Client) AuthorizeURL(state string) string {
+	base := strings.TrimRight(c.cfg.MciasURL, "/")
+	return base + "/sso/authorize?" + url.Values{
+		"client_id":    {c.cfg.ClientID},
+		"redirect_uri": {c.cfg.RedirectURI},
+		"state":        {state},
+	}.Encode()
+}
+
+// ExchangeCode exchanges an authorization code for a JWT token by calling
+// MCIAS POST /v1/sso/token.
+func (c *Client) ExchangeCode(ctx context.Context, code string) (token string, expiresAt time.Time, err error) {
+	reqBody, _ := json.Marshal(map[string]string{
+		"code":         code,
+		"client_id":    c.cfg.ClientID,
+		"redirect_uri": c.cfg.RedirectURI,
+	})
+
+	base := strings.TrimRight(c.cfg.MciasURL, "/")
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost,
+		base+"/v1/sso/token", bytes.NewReader(reqBody))
+	if err != nil {
+		return "", time.Time{}, fmt.Errorf("sso: build exchange request: %w", err)
+	}
+	req.Header.Set("Content-Type", "application/json")
+
+	resp, err := c.httpClient.Do(req)
+	if err != nil {
+		return "", time.Time{}, fmt.Errorf("sso: MCIAS exchange: %w", err)
+	}
+	defer func() { _ = resp.Body.Close() }()
+
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return "", time.Time{}, fmt.Errorf("sso: read exchange response: %w", err)
+	}
+
+	if resp.StatusCode != http.StatusOK {
+		return "", time.Time{}, fmt.Errorf("sso: exchange failed (HTTP %d): %s", resp.StatusCode, body)
+	}
+
+	var result struct {
+		Token     string `json:"token"`
+		ExpiresAt string `json:"expires_at"`
+	}
+	if err := json.Unmarshal(body, &result); err != nil {
+		return "", time.Time{}, fmt.Errorf("sso: decode exchange response: %w", err)
+	}
+
+	exp, parseErr := time.Parse(time.RFC3339, result.ExpiresAt)
+	if parseErr != nil {
+		exp = time.Now().Add(1 * time.Hour)
+	}
+
+	return result.Token, exp, nil
+}
+
+// GenerateState returns a cryptographically random hex-encoded state string.
+func GenerateState() (string, error) {
+	raw := make([]byte, stateBytes)
+	if _, err := rand.Read(raw); err != nil {
+		return "", fmt.Errorf("sso: generate state: %w", err)
+	}
+	return hex.EncodeToString(raw), nil
+}
+
+// StateCookieName returns the cookie name used for SSO state for a given
+// service cookie prefix (e.g., "mcr" → "mcr_sso_state").
+func StateCookieName(prefix string) string {
+	return prefix + "_sso_state"
+}
+
+// ReturnToCookieName returns the cookie name used for SSO return-to URL
+// (e.g., "mcr" → "mcr_sso_return").
+func ReturnToCookieName(prefix string) string {
+	return prefix + "_sso_return"
+}
+
+// SetStateCookie stores the SSO state in a short-lived cookie.
+//
+// Security: SameSite=Lax is required because the redirect from MCIAS back to
+// the service is a cross-site top-level navigation. SameSite=Strict cookies
+// would not be sent on that redirect.
+func SetStateCookie(w http.ResponseWriter, prefix, state string) {
+	http.SetCookie(w, &http.Cookie{
+		Name:     StateCookieName(prefix),
+		Value:    state,
+		Path:     "/",
+		MaxAge:   stateCookieAge,
+		HttpOnly: true,
+		Secure:   true,
+		SameSite: http.SameSiteLaxMode,
+	})
+}
+
+// ValidateStateCookie compares the state query parameter against the state
+// cookie. If they match, the cookie is cleared and nil is returned.
+func ValidateStateCookie(w http.ResponseWriter, r *http.Request, prefix, queryState string) error {
+	c, err := r.Cookie(StateCookieName(prefix))
+	if err != nil || c.Value == "" {
+		return fmt.Errorf("sso: missing state cookie")
+	}
+
+	if c.Value != queryState {
+		return fmt.Errorf("sso: state mismatch")
+	}
+
+	// Clear the state cookie (single-use).
+	http.SetCookie(w, &http.Cookie{
+		Name:     StateCookieName(prefix),
+		Value:    "",
+		Path:     "/",
+		MaxAge:   -1,
+		HttpOnly: true,
+		Secure:   true,
+		SameSite: http.SameSiteLaxMode,
+	})
+
+	return nil
+}
+
+// SetReturnToCookie stores the current request path so the service can
+// redirect back to it after SSO login completes.
+func SetReturnToCookie(w http.ResponseWriter, r *http.Request, prefix string) {
+	path := r.URL.Path
+	if path == "" || path == "/login" || strings.HasPrefix(path, "/sso/") {
+		path = "/"
+	}
+	http.SetCookie(w, &http.Cookie{
+		Name:     ReturnToCookieName(prefix),
+		Value:    path,
+		Path:     "/",
+		MaxAge:   stateCookieAge,
+		HttpOnly: true,
+		Secure:   true,
+		SameSite: http.SameSiteLaxMode,
+	})
+}
+
+// ConsumeReturnToCookie reads and clears the return-to cookie, returning
+// the path. Returns "/" if the cookie is missing or empty.
+func ConsumeReturnToCookie(w http.ResponseWriter, r *http.Request, prefix string) string {
+	c, err := r.Cookie(ReturnToCookieName(prefix))
+	path := "/"
+	if err == nil && c.Value != "" {
+		path = c.Value
+	}
+
+	// Clear the cookie.
+	http.SetCookie(w, &http.Cookie{
+		Name:     ReturnToCookieName(prefix),
+		Value:    "",
+		Path:     "/",
+		MaxAge:   -1,
+		HttpOnly: true,
+		Secure:   true,
+		SameSite: http.SameSiteLaxMode,
+	})
+
+	return path
+}
+
+// RedirectToLogin generates a state, sets the state and return-to cookies,
+// and redirects the user to the MCIAS authorize URL.
+func RedirectToLogin(w http.ResponseWriter, r *http.Request, client *Client, cookiePrefix string) error {
+	state, err := GenerateState()
+	if err != nil {
+		return err
+	}
+
+	SetStateCookie(w, cookiePrefix, state)
+	SetReturnToCookie(w, r, cookiePrefix)
+	http.Redirect(w, r, client.AuthorizeURL(state), http.StatusFound)
+	return nil
+}
+
+// HandleCallback validates the state, exchanges the authorization code for
+// a JWT, and returns the token and the return-to path. The caller should
+// set the session cookie with the returned token.
+func HandleCallback(w http.ResponseWriter, r *http.Request, client *Client, cookiePrefix string) (token, returnTo string, err error) {
+	code := r.URL.Query().Get("code")
+	state := r.URL.Query().Get("state")
+	if code == "" || state == "" {
+		return "", "", fmt.Errorf("sso: missing code or state parameter")
+	}
+
+	if err := ValidateStateCookie(w, r, cookiePrefix, state); err != nil {
+		return "", "", err
+	}
+
+	token, _, err = client.ExchangeCode(r.Context(), code)
+	if err != nil {
+		return "", "", err
+	}
+
+	returnTo = ConsumeReturnToCookie(w, r, cookiePrefix)
+	return token, returnTo, nil
+}

sso/sso_test.go

@@ -0,0 +1,225 @@
+package sso
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestNewValidation(t *testing.T) {
+	tests := []struct {
+		name    string
+		cfg     Config
+		wantErr bool
+	}{
+		{"valid", Config{MciasURL: "https://mcias.example.com", ClientID: "mcr", RedirectURI: "https://mcr.example.com/cb"}, false},
+		{"missing url", Config{ClientID: "mcr", RedirectURI: "https://mcr.example.com/cb"}, true},
+		{"missing client_id", Config{MciasURL: "https://mcias.example.com", RedirectURI: "https://mcr.example.com/cb"}, true},
+		{"missing redirect_uri", Config{MciasURL: "https://mcias.example.com", ClientID: "mcr"}, true},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			_, err := New(tc.cfg)
+			if tc.wantErr && err == nil {
+				t.Error("expected error, got nil")
+			}
+			if !tc.wantErr && err != nil {
+				t.Errorf("unexpected error: %v", err)
+			}
+		})
+	}
+}
+
+func TestAuthorizeURL(t *testing.T) {
+	c, err := New(Config{
+		MciasURL:    "http://localhost:8443",
+		ClientID:    "mcr",
+		RedirectURI: "https://mcr.example.com/sso/callback",
+	})
+	if err != nil {
+		t.Fatalf("New: %v", err)
+	}
+
+	u := c.AuthorizeURL("test-state")
+	if u == "" {
+		t.Fatal("AuthorizeURL returned empty string")
+	}
+
+	// Should contain all required params.
+	for _, want := range []string{"client_id=mcr", "state=test-state", "redirect_uri="} {
+		if !contains(u, want) {
+			t.Errorf("URL %q missing %q", u, want)
+		}
+	}
+}
+
+func TestExchangeCode(t *testing.T) {
+	// Fake MCIAS server.
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/v1/sso/token" {
+			http.Error(w, "not found", http.StatusNotFound)
+			return
+		}
+		if r.Method != http.MethodPost {
+			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+			return
+		}
+
+		var req struct {
+			Code        string `json:"code"`
+			ClientID    string `json:"client_id"`
+			RedirectURI string `json:"redirect_uri"`
+		}
+		if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+			http.Error(w, "bad request", http.StatusBadRequest)
+			return
+		}
+
+		if req.Code != "valid-code" {
+			http.Error(w, `{"error":"invalid code"}`, http.StatusUnauthorized)
+			return
+		}
+
+		w.Header().Set("Content-Type", "application/json")
+		_ = json.NewEncoder(w).Encode(map[string]string{
+			"token":      "jwt-token-here",
+			"expires_at": "2026-03-30T23:00:00Z",
+		})
+	}))
+	defer srv.Close()
+
+	c, err := New(Config{
+		MciasURL:    srv.URL,
+		ClientID:    "mcr",
+		RedirectURI: "https://mcr.example.com/cb",
+	})
+	if err != nil {
+		t.Fatalf("New: %v", err)
+	}
+
+	// Valid code.
+	token, _, err := c.ExchangeCode(t.Context(), "valid-code")
+	if err != nil {
+		t.Fatalf("ExchangeCode: %v", err)
+	}
+	if token != "jwt-token-here" {
+		t.Errorf("token = %q, want %q", token, "jwt-token-here")
+	}
+
+	// Invalid code.
+	_, _, err = c.ExchangeCode(t.Context(), "bad-code")
+	if err == nil {
+		t.Error("expected error for bad code")
+	}
+}
+
+func TestGenerateState(t *testing.T) {
+	s1, err := GenerateState()
+	if err != nil {
+		t.Fatalf("GenerateState: %v", err)
+	}
+	if len(s1) != 64 { // 32 bytes = 64 hex chars
+		t.Errorf("state length = %d, want 64", len(s1))
+	}
+
+	s2, err := GenerateState()
+	if err != nil {
+		t.Fatalf("GenerateState: %v", err)
+	}
+	if s1 == s2 {
+		t.Error("two states should differ")
+	}
+}
+
+func TestStateCookieRoundTrip(t *testing.T) {
+	state := "test-state-value"
+	rec := httptest.NewRecorder()
+	SetStateCookie(rec, "mcr", state)
+
+	// Simulate a request with the cookie.
+	req := httptest.NewRequest(http.MethodGet, "/sso/callback?state="+state, nil)
+	for _, c := range rec.Result().Cookies() {
+		req.AddCookie(c)
+	}
+
+	w := httptest.NewRecorder()
+	if err := ValidateStateCookie(w, req, "mcr", state); err != nil {
+		t.Fatalf("ValidateStateCookie: %v", err)
+	}
+}
+
+func TestStateCookieMismatch(t *testing.T) {
+	rec := httptest.NewRecorder()
+	SetStateCookie(rec, "mcr", "correct-state")
+
+	req := httptest.NewRequest(http.MethodGet, "/sso/callback?state=wrong-state", nil)
+	for _, c := range rec.Result().Cookies() {
+		req.AddCookie(c)
+	}
+
+	w := httptest.NewRecorder()
+	if err := ValidateStateCookie(w, req, "mcr", "wrong-state"); err == nil {
+		t.Error("expected error for state mismatch")
+	}
+}
+
+func TestReturnToCookie(t *testing.T) {
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequest(http.MethodGet, "/repositories/myrepo", nil)
+	SetReturnToCookie(rec, req, "mcr")
+
+	// Read back.
+	req2 := httptest.NewRequest(http.MethodGet, "/sso/callback", nil)
+	for _, c := range rec.Result().Cookies() {
+		req2.AddCookie(c)
+	}
+
+	w2 := httptest.NewRecorder()
+	path := ConsumeReturnToCookie(w2, req2, "mcr")
+	if path != "/repositories/myrepo" {
+		t.Errorf("return-to = %q, want %q", path, "/repositories/myrepo")
+	}
+}
+
+func TestReturnToDefaultsToRoot(t *testing.T) {
+	req := httptest.NewRequest(http.MethodGet, "/sso/callback", nil)
+	w := httptest.NewRecorder()
+	path := ConsumeReturnToCookie(w, req, "mcr")
+	if path != "/" {
+		t.Errorf("return-to = %q, want %q", path, "/")
+	}
+}
+
+func TestReturnToSkipsLoginPaths(t *testing.T) {
+	for _, p := range []string{"/login", "/sso/callback", "/sso/redirect"} {
+		rec := httptest.NewRecorder()
+		req := httptest.NewRequest(http.MethodGet, p, nil)
+		SetReturnToCookie(rec, req, "mcr")
+
+		req2 := httptest.NewRequest(http.MethodGet, "/sso/callback", nil)
+		for _, c := range rec.Result().Cookies() {
+			req2.AddCookie(c)
+		}
+
+		w2 := httptest.NewRecorder()
+		path := ConsumeReturnToCookie(w2, req2, "mcr")
+		if path != "/" {
+			t.Errorf("return-to for %s = %q, want %q", p, path, "/")
+		}
+	}
+}
+
+func contains(s, sub string) bool {
+	return len(s) >= len(sub) && (s == sub || len(s) > 0 && containsStr(s, sub))
+}
+
+func containsStr(s, sub string) bool {
+	for i := 0; i <= len(s)-len(sub); i++ {
+		if s[i:i+len(sub)] == sub {
+			return true
+		}
+	}
+	return false
+}

terminal/terminal.go

@@ -0,0 +1,36 @@
+// Package terminal provides secure terminal input helpers for CLI tools.
+package terminal
+
+import (
+	"fmt"
+	"os"
+
+	"golang.org/x/term"
+)
+
+// ReadPassword prints the given prompt to stderr and reads a password
+// from the terminal with echo disabled. It prints a newline after the
+// input is complete so the cursor advances normally.
+func ReadPassword(prompt string) (string, error) {
+	b, err := readRaw(prompt)
+	if err != nil {
+		return "", err
+	}
+	return string(b), nil
+}
+
+// ReadPasswordBytes is like ReadPassword but returns a []byte so the
+// caller can zeroize the buffer after use.
+func ReadPasswordBytes(prompt string) ([]byte, error) {
+	return readRaw(prompt)
+}
+
+func readRaw(prompt string) ([]byte, error) {
+	fmt.Fprint(os.Stderr, prompt)
+	b, err := term.ReadPassword(int(os.Stdin.Fd())) //nolint:gosec // fd fits in int
+	fmt.Fprintln(os.Stderr)
+	if err != nil {
+		return nil, err
+	}
+	return b, nil
+}

terminal/terminal_test.go

@@ -0,0 +1,21 @@
+package terminal
+
+import (
+	"testing"
+)
+
+func TestReadPasswordNotATTY(t *testing.T) {
+	// When stdin is not a terminal (e.g. in CI), ReadPassword should
+	// return an error rather than hanging or panicking.
+	_, err := ReadPassword("Password: ")
+	if err == nil {
+		t.Fatal("expected error when stdin is not a terminal")
+	}
+}
+
+func TestReadPasswordBytesNotATTY(t *testing.T) {
+	_, err := ReadPasswordBytes("Password: ")
+	if err == nil {
+		t.Fatal("expected error when stdin is not a terminal")
+	}
+}

web/web.go

@@ -8,7 +8,7 @@ import (
 	"io/fs"
 	"net/http"
 
-	"git.wntrmute.dev/kyle/mcdsl/auth"
+	"git.wntrmute.dev/mc/mcdsl/auth"
 )
 
 // SetSessionCookie sets a session cookie with the standard Metacircular

web/web_test.go

@@ -9,7 +9,7 @@ import (
 	"testing"
 	"testing/fstest"
 
-	"git.wntrmute.dev/kyle/mcdsl/auth"
+	"git.wntrmute.dev/mc/mcdsl/auth"
 )
 
 func TestSetSessionCookie(t *testing.T) {