oidcauth.go

v1.1.0

package oidcauth

import (
	"context"
	"crypto/hmac"
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"encoding/json"
	"fmt"
	"net/http"
	"time"

	"github.com/coreos/go-oidc/v3/oidc"
	"golang.org/x/oauth2"

	"example.com/curator/internal/config"
)

const (
	stateCookieName   = "curator_oidc_state"
	sessionCookieName = "curator_session"
	sessionDuration   = 8 * time.Hour
)

// Provider handles OIDC authentication for the admin UI.
type Provider struct {
	oauth2Cfg  oauth2.Config
	verifier   *oidc.IDTokenVerifier
	sessionKey []byte // HMAC key derived from client secret
}

// New creates an OIDC provider by performing discovery on the issuer.
func New(ctx context.Context, cfg *config.OIDCConfig, clientSecret string) (*Provider, error) {
	provider, err := oidc.NewProvider(ctx, cfg.Issuer)
	if err != nil {
		return nil, fmt.Errorf("oidc discovery: %w", err)
	}

	oauth2Cfg := oauth2.Config{
		ClientID:     cfg.ClientID,
		ClientSecret: clientSecret,
		RedirectURL:  cfg.RedirectURL,
		Endpoint:     provider.Endpoint(),
		Scopes:       []string{oidc.ScopeOpenID, "profile", "email"},
	}

	verifier := provider.Verifier(&oidc.Config{ClientID: cfg.ClientID})

	// Derive session signing key from client secret via SHA-256.
	key := sha256.Sum256([]byte("curator-session:" + clientSecret))

	return &Provider{
		oauth2Cfg:  oauth2Cfg,
		verifier:   verifier,
		sessionKey: key[:],
	}, nil
}

// LoginHandler redirects to the OIDC provider's authorization endpoint.
func (p *Provider) LoginHandler(w http.ResponseWriter, r *http.Request) {
	state := randomString(32)

	http.SetCookie(w, &http.Cookie{
		Name:     stateCookieName,
		Value:    state,
		Path:     "/-/oidc/",
		MaxAge:   300, // 5 minutes
		HttpOnly: true,
		SameSite: http.SameSiteLaxMode,
		Secure:   r.TLS != nil,
	})

	http.Redirect(w, r, p.oauth2Cfg.AuthCodeURL(state, oauth2.S256ChallengeOption(state)), http.StatusFound)
}

// CallbackHandler handles the OIDC callback, exchanges the code, and sets a session cookie.
func (p *Provider) CallbackHandler(w http.ResponseWriter, r *http.Request) {
	// Validate state.
	stateCookie, err := r.Cookie(stateCookieName)
	if err != nil || stateCookie.Value == "" {
		http.Error(w, "missing state cookie", http.StatusBadRequest)
		return
	}
	if r.URL.Query().Get("state") != stateCookie.Value {
		http.Error(w, "state mismatch", http.StatusBadRequest)
		return
	}

	// Clear state cookie.
	http.SetCookie(w, &http.Cookie{
		Name:   stateCookieName,
		Path:   "/-/oidc/",
		MaxAge: -1,
	})

	// Check for error response from provider.
	if errCode := r.URL.Query().Get("error"); errCode != "" {
		desc := r.URL.Query().Get("error_description")
		http.Error(w, fmt.Sprintf("oidc error: %s: %s", errCode, desc), http.StatusForbidden)
		return
	}

	// Exchange code for tokens.
	token, err := p.oauth2Cfg.Exchange(r.Context(), r.URL.Query().Get("code"),
		oauth2.VerifierOption(stateCookie.Value))
	if err != nil {
		http.Error(w, "token exchange failed", http.StatusInternalServerError)
		return
	}

	// Extract and verify ID token.
	rawIDToken, ok := token.Extra("id_token").(string)
	if !ok {
		http.Error(w, "missing id_token", http.StatusInternalServerError)
		return
	}

	idToken, err := p.verifier.Verify(r.Context(), rawIDToken)
	if err != nil {
		http.Error(w, "id_token verification failed", http.StatusForbidden)
		return
	}

	var claims struct {
		Sub   string `json:"sub"`
		Email string `json:"email"`
		Name  string `json:"name"`
	}
	if err := idToken.Claims(&claims); err != nil {
		http.Error(w, "failed to parse claims", http.StatusInternalServerError)
		return
	}

	// Create session cookie.
	sessionValue, err := p.signSession(claims.Sub, claims.Email)
	if err != nil {
		http.Error(w, "session creation failed", http.StatusInternalServerError)
		return
	}

	http.SetCookie(w, &http.Cookie{
		Name:     sessionCookieName,
		Value:    sessionValue,
		Path:     "/-/",
		MaxAge:   int(sessionDuration.Seconds()),
		HttpOnly: true,
		SameSite: http.SameSiteLaxMode,
		Secure:   r.TLS != nil,
	})

	http.Redirect(w, r, "/-/admin/", http.StatusFound)
}

// LogoutHandler clears the session cookie and redirects to the admin login.
func (p *Provider) LogoutHandler(w http.ResponseWriter, r *http.Request) {
	http.SetCookie(w, &http.Cookie{
		Name:   sessionCookieName,
		Path:   "/-/",
		MaxAge: -1,
	})
	http.Redirect(w, r, "/-/admin/", http.StatusFound)
}

// session is the JSON payload stored in the session cookie.
type session struct {
	Sub   string `json:"sub"`
	Email string `json:"email"`
	Exp   int64  `json:"exp"`
}

// signSession creates an HMAC-signed session cookie value.
func (p *Provider) signSession(sub, email string) (string, error) {
	s := session{
		Sub:   sub,
		Email: email,
		Exp:   time.Now().Add(sessionDuration).Unix(),
	}

	payload, err := json.Marshal(s)
	if err != nil {
		return "", err
	}

	mac := hmac.New(sha256.New, p.sessionKey)
	mac.Write(payload)
	sig := mac.Sum(nil)

	// payload.signature, both base64url encoded.
	return base64.RawURLEncoding.EncodeToString(payload) + "." +
		base64.RawURLEncoding.EncodeToString(sig), nil
}

// ValidateSession verifies an HMAC-signed session cookie value.
// Returns the email on success or an empty string on failure.
func (p *Provider) ValidateSession(value string) string {
	dot := -1
	for i := len(value) - 1; i >= 0; i-- {
		if value[i] == '.' {
			dot = i
			break
		}
	}
	if dot < 0 {
		return ""
	}

	payload, err := base64.RawURLEncoding.DecodeString(value[:dot])
	if err != nil {
		return ""
	}
	sig, err := base64.RawURLEncoding.DecodeString(value[dot+1:])
	if err != nil {
		return ""
	}

	mac := hmac.New(sha256.New, p.sessionKey)
	mac.Write(payload)
	if !hmac.Equal(sig, mac.Sum(nil)) {
		return ""
	}

	var s session
	if err := json.Unmarshal(payload, &s); err != nil {
		return ""
	}
	if time.Now().Unix() > s.Exp {
		return ""
	}

	return s.Email
}

func randomString(n int) string {
	b := make([]byte, n)
	rand.Read(b)
	return base64.RawURLEncoding.EncodeToString(b)
}


Source Files

oidcauth.go

1	package oidcauth
2
3	import (
4	"context"
5	"crypto/hmac"
6	"crypto/rand"
7	"crypto/sha256"
8	"encoding/base64"
9	"encoding/json"
10	"fmt"
11	"net/http"
12	"time"
13
14	"github.com/coreos/go-oidc/v3/oidc"
15	"golang.org/x/oauth2"
16
17	"example.com/curator/internal/config"
18	)
19
20	const (
21	stateCookieName = "curator_oidc_state"
22	sessionCookieName = "curator_session"
23	sessionDuration = 8 * time.Hour
24	)
25
26	// Provider handles OIDC authentication for the admin UI.
27	type Provider struct {
28	oauth2Cfg oauth2.Config
29	verifier *oidc.IDTokenVerifier
30	sessionKey []byte // HMAC key derived from client secret
31	}
32
33	// New creates an OIDC provider by performing discovery on the issuer.
34	func New(ctx context.Context, cfg config.OIDCConfig, clientSecret string) (Provider, error) {
35	provider, err := oidc.NewProvider(ctx, cfg.Issuer)
36	if err != nil {
37	return nil, fmt.Errorf("oidc discovery: %w", err)
38	}
39
40	oauth2Cfg := oauth2.Config{
41	ClientID: cfg.ClientID,
42	ClientSecret: clientSecret,
43	RedirectURL: cfg.RedirectURL,
44	Endpoint: provider.Endpoint(),
45	Scopes: []string{oidc.ScopeOpenID, "profile", "email"},
46	}
47
48	verifier := provider.Verifier(&oidc.Config{ClientID: cfg.ClientID})
49
50	// Derive session signing key from client secret via SHA-256.
51	key := sha256.Sum256([]byte("curator-session:" + clientSecret))
52
53	return &Provider{
54	oauth2Cfg: oauth2Cfg,
55	verifier: verifier,
56	sessionKey: key[:],
57	}, nil
58	}
59
60	// LoginHandler redirects to the OIDC provider's authorization endpoint.
61	func (p Provider) LoginHandler(w http.ResponseWriter, r http.Request) {
62	state := randomString(32)
63
64	http.SetCookie(w, &http.Cookie{
65	Name: stateCookieName,
66	Value: state,
67	Path: "/-/oidc/",
68	MaxAge: 300, // 5 minutes
69	HttpOnly: true,
70	SameSite: http.SameSiteLaxMode,
71	Secure: r.TLS != nil,
72	})
73
74	http.Redirect(w, r, p.oauth2Cfg.AuthCodeURL(state, oauth2.S256ChallengeOption(state)), http.StatusFound)
75	}
76
77	// CallbackHandler handles the OIDC callback, exchanges the code, and sets a session cookie.
78	func (p Provider) CallbackHandler(w http.ResponseWriter, r http.Request) {
79	// Validate state.
80	stateCookie, err := r.Cookie(stateCookieName)
81	if err != nil \|\| stateCookie.Value == "" {
82	http.Error(w, "missing state cookie", http.StatusBadRequest)
83	return
84	}
85	if r.URL.Query().Get("state") != stateCookie.Value {
86	http.Error(w, "state mismatch", http.StatusBadRequest)
87	return
88	}
89
90	// Clear state cookie.
91	http.SetCookie(w, &http.Cookie{
92	Name: stateCookieName,
93	Path: "/-/oidc/",
94	MaxAge: -1,
95	})
96
97	// Check for error response from provider.
98	if errCode := r.URL.Query().Get("error"); errCode != "" {
99	desc := r.URL.Query().Get("error_description")
100	http.Error(w, fmt.Sprintf("oidc error: %s: %s", errCode, desc), http.StatusForbidden)
101	return
102	}
103
104	// Exchange code for tokens.
105	token, err := p.oauth2Cfg.Exchange(r.Context(), r.URL.Query().Get("code"),
106	oauth2.VerifierOption(stateCookie.Value))
107	if err != nil {
108	http.Error(w, "token exchange failed", http.StatusInternalServerError)
109	return
110	}
111
112	// Extract and verify ID token.
113	rawIDToken, ok := token.Extra("id_token").(string)
114	if !ok {
115	http.Error(w, "missing id_token", http.StatusInternalServerError)
116	return
117	}
118
119	idToken, err := p.verifier.Verify(r.Context(), rawIDToken)
120	if err != nil {
121	http.Error(w, "id_token verification failed", http.StatusForbidden)
122	return
123	}
124
125	var claims struct {
126	Sub string `json:"sub"`
127	Email string `json:"email"`
128	Name string `json:"name"`
129	}
130	if err := idToken.Claims(&claims); err != nil {
131	http.Error(w, "failed to parse claims", http.StatusInternalServerError)
132	return
133	}
134
135	// Create session cookie.
136	sessionValue, err := p.signSession(claims.Sub, claims.Email)
137	if err != nil {
138	http.Error(w, "session creation failed", http.StatusInternalServerError)
139	return
140	}
141
142	http.SetCookie(w, &http.Cookie{
143	Name: sessionCookieName,
144	Value: sessionValue,
145	Path: "/-/",
146	MaxAge: int(sessionDuration.Seconds()),
147	HttpOnly: true,
148	SameSite: http.SameSiteLaxMode,
149	Secure: r.TLS != nil,
150	})
151
152	http.Redirect(w, r, "/-/admin/", http.StatusFound)
153	}
154
155	// LogoutHandler clears the session cookie and redirects to the admin login.
156	func (p Provider) LogoutHandler(w http.ResponseWriter, r http.Request) {
157	http.SetCookie(w, &http.Cookie{
158	Name: sessionCookieName,
159	Path: "/-/",
160	MaxAge: -1,
161	})
162	http.Redirect(w, r, "/-/admin/", http.StatusFound)
163	}
164
165	// session is the JSON payload stored in the session cookie.
166	type session struct {
167	Sub string `json:"sub"`
168	Email string `json:"email"`
169	Exp int64 `json:"exp"`
170	}
171
172	// signSession creates an HMAC-signed session cookie value.
173	func (p *Provider) signSession(sub, email string) (string, error) {
174	s := session{
175	Sub: sub,
176	Email: email,
177	Exp: time.Now().Add(sessionDuration).Unix(),
178	}
179
180	payload, err := json.Marshal(s)
181	if err != nil {
182	return "", err
183	}
184
185	mac := hmac.New(sha256.New, p.sessionKey)
186	mac.Write(payload)
187	sig := mac.Sum(nil)
188
189	// payload.signature, both base64url encoded.
190	return base64.RawURLEncoding.EncodeToString(payload) + "." +
191	base64.RawURLEncoding.EncodeToString(sig), nil
192	}
193
194	// ValidateSession verifies an HMAC-signed session cookie value.
195	// Returns the email on success or an empty string on failure.
196	func (p *Provider) ValidateSession(value string) string {
197	dot := -1
198	for i := len(value) - 1; i >= 0; i-- {
199	if value[i] == '.' {
200	dot = i
201	break
202	}
203	}
204	if dot < 0 {
205	return ""
206	}
207
208	payload, err := base64.RawURLEncoding.DecodeString(value[:dot])
209	if err != nil {
210	return ""
211	}
212	sig, err := base64.RawURLEncoding.DecodeString(value[dot+1:])
213	if err != nil {
214	return ""
215	}
216
217	mac := hmac.New(sha256.New, p.sessionKey)
218	mac.Write(payload)
219	if !hmac.Equal(sig, mac.Sum(nil)) {
220	return ""
221	}
222
223	var s session
224	if err := json.Unmarshal(payload, &s); err != nil {
225	return ""
226	}
227	if time.Now().Unix() > s.Exp {
228	return ""
229	}
230
231	return s.Email
232	}
233
234	func randomString(n int) string {
235	b := make([]byte, n)
236	rand.Read(b)
237	return base64.RawURLEncoding.EncodeToString(b)
238	}
239