core/identity: dynamic authenticator registration (#5105)

pkg/identity/oauth/github/github.go

@@ -0,0 +1,258 @@
+// Package github implements OAuth2 based authentication for github
+//
+// https://www.pomerium.com/docs/identity-providers/github
+package github
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/http"
+	"net/url"
+	"strings"
+	"time"
+
+	"github.com/go-jose/go-jose/v3/jwt"
+	"golang.org/x/oauth2"
+
+	"github.com/pomerium/pomerium/internal/httputil"
+	"github.com/pomerium/pomerium/internal/log"
+	"github.com/pomerium/pomerium/internal/urlutil"
+	"github.com/pomerium/pomerium/internal/version"
+	"github.com/pomerium/pomerium/pkg/identity/identity"
+	"github.com/pomerium/pomerium/pkg/identity/oauth"
+	"github.com/pomerium/pomerium/pkg/identity/oidc"
+)
+
+// Name identifies the GitHub identity provider
+const Name = "github"
+
+const (
+	defaultProviderURL = "https://github.com"
+	githubAPIURL       = "https://api.github.com"
+	userPath           = "/user"
+	revokePath         = "/applications/%s/grant"
+	emailPath          = "/user/emails"
+	// https://developer.github.com/apps/building-oauth-apps/authorizing-oauth-apps
+	authURL  = "/login/oauth/authorize"
+	tokenURL = "/login/oauth/access_token" //nolint:gosec
+
+	// since github doesn't implement oidc, we need this to refresh the user session
+	refreshDeadline = time.Minute * 60
+)
+
+var maxTime = time.Unix(253370793661, 0) // year 9999
+
+// https://developer.github.com/apps/building-oauth-apps/understanding-scopes-for-oauth-apps/
+var defaultScopes = []string{"user:email", "read:org"}
+
+// Provider is an implementation of the OAuth Provider.
+type Provider struct {
+	Oauth *oauth2.Config
+
+	userEndpoint  string
+	emailEndpoint string
+}
+
+// New instantiates an OAuth2 provider for Github.
+func New(_ context.Context, o *oauth.Options) (*Provider, error) {
+	p := Provider{}
+	if o.ProviderURL == "" {
+		o.ProviderURL = defaultProviderURL
+	}
+
+	// when the default provider url is used, use the Github API endpoint
+	if o.ProviderURL == defaultProviderURL {
+		p.userEndpoint = urlutil.Join(githubAPIURL, userPath)
+		p.emailEndpoint = urlutil.Join(githubAPIURL, emailPath)
+	} else {
+		p.userEndpoint = urlutil.Join(o.ProviderURL, userPath)
+		p.emailEndpoint = urlutil.Join(o.ProviderURL, emailPath)
+	}
+
+	if len(o.Scopes) == 0 {
+		o.Scopes = defaultScopes
+	}
+	p.Oauth = &oauth2.Config{
+		ClientID:     o.ClientID,
+		ClientSecret: o.ClientSecret,
+		Scopes:       o.Scopes,
+		RedirectURL:  o.RedirectURL.String(),
+		Endpoint: oauth2.Endpoint{
+			AuthURL:  urlutil.Join(o.ProviderURL, authURL),
+			TokenURL: urlutil.Join(o.ProviderURL, tokenURL),
+		},
+	}
+	return &p, nil
+}
+
+// Authenticate creates an identity session with github from a authorization code, and follows up
+// call to the user and user group endpoint with the
+func (p *Provider) Authenticate(ctx context.Context, code string, v identity.State) (*oauth2.Token, error) {
+	oauth2Token, err := p.Oauth.Exchange(ctx, code)
+	if err != nil {
+		return nil, fmt.Errorf("github: token exchange failed %w", err)
+	}
+
+	// github tokens never expire
+	oauth2Token.Expiry = maxTime
+
+	err = p.UpdateUserInfo(ctx, oauth2Token, v)
+	if err != nil {
+		return nil, err
+	}
+
+	return oauth2Token, nil
+}
+
+// UpdateUserInfo will get the user information from github and also retrieve the user's team(s)
+//
+// https://developer.github.com/v3/users/#get-the-authenticated-user
+func (p *Provider) UpdateUserInfo(ctx context.Context, t *oauth2.Token, v any) error {
+	err := p.userInfo(ctx, t, v)
+	if err != nil {
+		return fmt.Errorf("github: could not retrieve user info %w", err)
+	}
+
+	err = p.userEmail(ctx, t, v)
+	if err != nil {
+		return fmt.Errorf("github: could not retrieve user email %w", err)
+	}
+
+	return nil
+}
+
+// Refresh is a no-op for github, because github sessions never expire.
+func (p *Provider) Refresh(_ context.Context, t *oauth2.Token, _ identity.State) (*oauth2.Token, error) {
+	t.Expiry = time.Now().Add(refreshDeadline)
+	return t, nil
+}
+
+// userEmail returns the primary email of the user by making
+// a query to github API.
+//
+// https://developer.github.com/v3/users/emails/#list-email-addresses-for-a-user
+// https://developer.github.com/v3/auth/
+func (p *Provider) userEmail(ctx context.Context, t *oauth2.Token, v any) error {
+	// response represents the github user email
+	// https://developer.github.com/v3/users/emails/#response
+	var response []struct {
+		Email      string `json:"email"`
+		Verified   bool   `json:"verified"`
+		Primary    bool   `json:"primary"`
+		Visibility string `json:"visibility"`
+	}
+	headers := map[string]string{"Authorization": fmt.Sprintf("token %s", t.AccessToken)}
+	err := httputil.Do(ctx, http.MethodGet, p.emailEndpoint, version.UserAgent(), headers, nil, &response)
+	if err != nil {
+		return err
+	}
+	var out struct {
+		Email    string `json:"email"`
+		Verified bool   `json:"email_verified"`
+	}
+	log.Debug(ctx).Interface("emails", response).Msg("github: user emails")
+	for _, email := range response {
+		if email.Primary && email.Verified {
+			out.Email = email.Email
+			out.Verified = true
+			break
+		}
+	}
+	b, err := json.Marshal(out)
+	if err != nil {
+		return err
+	}
+	return json.Unmarshal(b, v)
+}
+
+func (p *Provider) userInfo(ctx context.Context, t *oauth2.Token, v any) error {
+	var response struct {
+		ID        int    `json:"id"`
+		Login     string `json:"login"`
+		Name      string `json:"name"`
+		AvatarURL string `json:"avatar_url,omitempty"`
+	}
+
+	headers := map[string]string{
+		"Authorization": fmt.Sprintf("token %s", t.AccessToken),
+		"Accept":        "application/vnd.github.v3+json",
+	}
+	err := httputil.Do(ctx, http.MethodGet, p.userEndpoint, version.UserAgent(), headers, nil, &response)
+	if err != nil {
+		return err
+	}
+	var out struct {
+		Subject string `json:"sub"`
+		Name    string `json:"name,omitempty"`
+		User    string `json:"user"`
+		Picture string `json:"picture,omitempty"`
+		// needs to be set manually
+		Expiry    *jwt.NumericDate `json:"exp,omitempty"`
+		NotBefore *jwt.NumericDate `json:"nbf,omitempty"`
+		IssuedAt  *jwt.NumericDate `json:"iat,omitempty"`
+	}
+
+	out.Expiry = jwt.NewNumericDate(time.Now().Add(refreshDeadline))
+	out.NotBefore = jwt.NewNumericDate(time.Now())
+	out.IssuedAt = jwt.NewNumericDate(time.Now())
+
+	out.User = response.Login
+	out.Subject = response.Login
+	out.Name = response.Name
+	out.Picture = response.AvatarURL
+	b, err := json.Marshal(out)
+	if err != nil {
+		return err
+	}
+	return json.Unmarshal(b, v)
+}
+
+// Revoke method will remove all the github grants the user
+// gave pomerium application during authorization.
+//
+// https://developer.github.com/v3/apps/oauth_applications/#delete-an-app-authorization
+func (p *Provider) Revoke(ctx context.Context, token *oauth2.Token) error {
+	// build the basic authentication request
+	basicAuth := url.UserPassword(p.Oauth.ClientID, p.Oauth.ClientSecret)
+	revokeURL := url.URL{
+		Scheme: "https",
+		User:   basicAuth,
+		Host:   "api.github.com",
+		Path:   fmt.Sprintf(revokePath, p.Oauth.ClientID),
+	}
+	reqBody := strings.NewReader(fmt.Sprintf(`{"access_token": "%s"}`, token.AccessToken))
+	req, err := http.NewRequestWithContext(ctx, http.MethodDelete, revokeURL.String(), reqBody)
+	if err != nil {
+		return errors.New("github: could not create revoke request")
+	}
+
+	req.Header.Set("Content-Type", "application/json")
+	client := &http.Client{}
+	resp, err := client.Do(req)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+
+	return nil
+}
+
+// Name returns the provider name.
+func (p *Provider) Name() string {
+	return Name
+}
+
+// SignIn redirects to the OAuth 2.0 provider's consent page
+// that asks for permissions for the required scopes explicitly.
+func (p *Provider) SignIn(w http.ResponseWriter, r *http.Request, state string) error {
+	signInURL := p.Oauth.AuthCodeURL(state, oauth2.AccessTypeOffline)
+	httputil.Redirect(w, r, signInURL, http.StatusFound)
+	return nil
+}
+
+// SignOut is not implemented.
+func (p *Provider) SignOut(_ http.ResponseWriter, _ *http.Request, _, _, _ string) error {
+	return oidc.ErrSignoutNotImplemented
+}