[codex] add generic OAuth2 outgoing auth

app/auth/plugins/oauth2/outgoing.go

@@ -0,0 +1,335 @@
+package oauth2
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"sort"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+
+	authplugins "github.com/winhowes/AuthTranslator/app/auth"
+	"github.com/winhowes/AuthTranslator/app/secrets"
+)
+
+const refreshSkew = time.Minute
+
+// oauth2Params configures generic OAuth2 access-token acquisition for outgoing
+// requests. client_secret and refresh_token are secret references, not raw values.
+type oauth2Params struct {
+	TokenURL     string            `json:"token_url"`
+	GrantType    string            `json:"grant_type"`
+	ClientID     string            `json:"client_id"`
+	ClientSecret string            `json:"client_secret"`
+	RefreshToken string            `json:"refresh_token"`
+	Scope        string            `json:"scope"`
+	Audience     string            `json:"audience"`
+	ClientAuth   string            `json:"client_auth"`
+	Header       string            `json:"header"`
+	Prefix       string            `json:"prefix"`
+	ExtraParams  map[string]string `json:"extra_params"`
+}
+
+// OAuth2 obtains OAuth2 access tokens from a configurable token endpoint and
+// attaches them to outgoing requests.
+type OAuth2 struct{}
+
+// HTTPClient performs token endpoint HTTP requests. It can be swapped in tests.
+var HTTPClient = &http.Client{Timeout: 5 * time.Second}
+
+type cachedToken struct {
+	accessToken  string
+	refreshToken string
+	exp          time.Time
+}
+
+var tokenCache = struct {
+	sync.Mutex
+	m map[string]cachedToken
+}{m: make(map[string]cachedToken)}
+
+type tokenResponse struct {
+	AccessToken  string          `json:"access_token"`
+	TokenType    string          `json:"token_type"`
+	ExpiresIn    json.RawMessage `json:"expires_in"`
+	RefreshToken string          `json:"refresh_token"`
+}
+
+func (o *OAuth2) Name() string { return "oauth2" }
+
+func (o *OAuth2) RequiredParams() []string { return []string{"token_url"} }
+
+func (o *OAuth2) OptionalParams() []string {
+	return []string{
+		"grant_type",
+		"client_id",
+		"client_secret",
+		"refresh_token",
+		"scope",
+		"audience",
+		"client_auth",
+		"header",
+		"prefix",
+		"extra_params",
+	}
+}
+
+func (o *OAuth2) ParseParams(m map[string]interface{}) (interface{}, error) {
+	_, prefixSet := m["prefix"]
+
+	p, err := authplugins.ParseParams[oauth2Params](m)
+	if err != nil {
+		return nil, err
+	}
+	if p.TokenURL == "" {
+		return nil, fmt.Errorf("missing token_url")
+	}
+	u, err := url.Parse(p.TokenURL)
+	if err != nil || u.Scheme == "" || u.Host == "" {
+		return nil, fmt.Errorf("invalid token_url")
+	}
+	if p.GrantType == "" {
+		if p.RefreshToken != "" {
+			p.GrantType = "refresh_token"
+		} else {
+			p.GrantType = "client_credentials"
+		}
+	}
+	if p.ClientAuth == "" {
+		p.ClientAuth = "body"
+	}
+	if p.Header == "" {
+		p.Header = "Authorization"
+	}
+	if !prefixSet {
+		p.Prefix = "Bearer "
+	}
+	if err := validateOAuth2Params(p); err != nil {
+		return nil, err
+	}
+	return p, nil
+}
+
+func validateOAuth2Params(p *oauth2Params) error {
+	switch p.GrantType {
+	case "client_credentials":
+		if p.ClientID == "" || p.ClientSecret == "" {
+			return fmt.Errorf("client_credentials grant requires client_id and client_secret")
+		}
+	case "refresh_token":
+		if p.RefreshToken == "" {
+			return fmt.Errorf("refresh_token grant requires refresh_token")
+		}
+	default:
+		return fmt.Errorf("unsupported grant_type %q", p.GrantType)
+	}
+
+	switch p.ClientAuth {
+	case "body":
+		if p.ClientSecret != "" && p.ClientID == "" {
+			return fmt.Errorf("client_id is required with client_secret")
+		}
+	case "basic":
+		if p.ClientID == "" || p.ClientSecret == "" {
+			return fmt.Errorf("basic client_auth requires client_id and client_secret")
+		}
+	case "none":
+		if p.ClientSecret != "" {
+			return fmt.Errorf("client_secret cannot be used with client_auth none")
+		}
+	default:
+		return fmt.Errorf("unsupported client_auth %q", p.ClientAuth)
+	}
+
+	for k := range p.ExtraParams {
+		key := strings.ToLower(strings.TrimSpace(k))
+		if key == "" {
+			return fmt.Errorf("extra_params cannot contain empty keys")
+		}
+		switch key {
+		case "grant_type", "client_id", "client_secret", "refresh_token", "scope", "audience":
+			return fmt.Errorf("extra_params cannot override %q", key)
+		}
+	}
+	return nil
+}
+
+func (p *oauth2Params) SecretRefs() []string {
+	var refs []string
+	if p.ClientSecret != "" {
+		refs = append(refs, p.ClientSecret)
+	}
+	if p.RefreshToken != "" {
+		refs = append(refs, p.RefreshToken)
+	}
+	return refs
+}
+
+func (o *OAuth2) AddAuth(ctx context.Context, r *http.Request, params interface{}) error {
+	cfg, ok := params.(*oauth2Params)
+	if !ok {
+		return fmt.Errorf("invalid config")
+	}
+
+	key := cfg.cacheKey()
+	ct := getCachedToken(key)
+	if ct.accessToken == "" || time.Now().After(ct.exp.Add(-refreshSkew)) {
+		next, err := fetchToken(ctx, cfg, ct.refreshToken)
+		if err != nil {
+			return err
+		}
+		if next.refreshToken == "" {
+			next.refreshToken = ct.refreshToken
+		}
+		setCachedToken(key, next)
+		ct = next
+	}
+
+	r.Header.Set(cfg.Header, cfg.Prefix+ct.accessToken)
+	return nil
+}
+
+func fetchToken(ctx context.Context, cfg *oauth2Params, cachedRefreshToken string) (cachedToken, error) {
+	form := url.Values{}
+	form.Set("grant_type", cfg.GrantType)
+	if cfg.Scope != "" {
+		form.Set("scope", cfg.Scope)
+	}
+	if cfg.Audience != "" {
+		form.Set("audience", cfg.Audience)
+	}
+	for k, v := range cfg.ExtraParams {
+		form.Set(k, v)
+	}
+
+	clientSecret, err := loadSecretRef(ctx, cfg.ClientSecret)
+	if err != nil {
+		return cachedToken{}, err
+	}
+
+	if cfg.GrantType == "refresh_token" {
+		refreshToken := cachedRefreshToken
+		if refreshToken == "" {
+			refreshToken, err = loadSecretRef(ctx, cfg.RefreshToken)
+			if err != nil {
+				return cachedToken{}, err
+			}
+		}
+		form.Set("refresh_token", refreshToken)
+	}
+
+	switch cfg.ClientAuth {
+	case "body":
+		if cfg.ClientID != "" {
+			form.Set("client_id", cfg.ClientID)
+		}
+		if cfg.ClientSecret != "" {
+			form.Set("client_secret", clientSecret)
+		}
+	case "basic":
+		// Added below after the request is built.
+	case "none":
+		if cfg.ClientID != "" {
+			form.Set("client_id", cfg.ClientID)
+		}
+	}
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, cfg.TokenURL, strings.NewReader(form.Encode()))
+	if err != nil {
+		return cachedToken{}, err
+	}
+	req.Header.Set("Accept", "application/json")
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	if cfg.ClientAuth == "basic" {
+		req.SetBasicAuth(cfg.ClientID, clientSecret)
+	}
+
+	resp, err := HTTPClient.Do(req)
+	if err != nil {
+		return cachedToken{}, err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode < http.StatusOK || resp.StatusCode >= http.StatusMultipleChoices {
+		body, _ := io.ReadAll(io.LimitReader(resp.Body, 4096))
+		return cachedToken{}, fmt.Errorf("token request failed: %s: %s", resp.Status, strings.TrimSpace(string(body)))
+	}
+
+	var tr tokenResponse
+	if err := json.NewDecoder(resp.Body).Decode(&tr); err != nil {
+		return cachedToken{}, err
+	}
+	if tr.AccessToken == "" {
+		return cachedToken{}, fmt.Errorf("empty access token")
+	}
+
+	return cachedToken{
+		accessToken:  tr.AccessToken,
+		refreshToken: tr.RefreshToken,
+		exp:          time.Now().Add(parseExpiresIn(tr.ExpiresIn)),
+	}, nil
+}
+
+func loadSecretRef(ctx context.Context, ref string) (string, error) {
+	if ref == "" {
+		return "", nil
+	}
+	return secrets.LoadSecret(ctx, ref)
+}
+
+func parseExpiresIn(raw json.RawMessage) time.Duration {
+	if len(raw) == 0 {
+		return time.Minute
+	}
+	var seconds float64
+	if err := json.Unmarshal(raw, &seconds); err == nil && seconds > 0 {
+		return time.Duration(seconds * float64(time.Second))
+	}
+	var text string
+	if err := json.Unmarshal(raw, &text); err == nil {
+		if parsed, err := strconv.ParseFloat(text, 64); err == nil && parsed > 0 {
+			return time.Duration(parsed * float64(time.Second))
+		}
+	}
+	return time.Minute
+}
+
+func (p *oauth2Params) cacheKey() string {
+	parts := []string{
+		p.TokenURL,
+		p.GrantType,
+		p.ClientID,
+		p.ClientSecret,
+		p.RefreshToken,
+		p.Scope,
+		p.Audience,
+		p.ClientAuth,
+	}
+	keys := make([]string, 0, len(p.ExtraParams))
+	for k := range p.ExtraParams {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+	for _, k := range keys {
+		parts = append(parts, k+"="+p.ExtraParams[k])
+	}
+	return strings.Join(parts, "\x00")
+}
+
+func getCachedToken(key string) cachedToken {
+	tokenCache.Lock()
+	defer tokenCache.Unlock()
+	return tokenCache.m[key]
+}
+
+func setCachedToken(key string, tok cachedToken) {
+	tokenCache.Lock()
+	tokenCache.m[key] = tok
+	tokenCache.Unlock()
+}
+
+func init() { authplugins.RegisterOutgoing(&OAuth2{}) }