Oidc (#109)

* add oidc config

* inching forward with oidc idp

* lil webfingy fix

* bit more progress

* further oidc

* oidc now working

* document dex config

* replace broken images

* add additional credits

* tiny doc update

* update

* add oidc config

* inching forward with oidc idp

* bit more progress

* further oidc

* oidc now working

* document dex config

* replace broken images

* add additional credits

* tiny doc update

* update

* document

* docs + comments

3 files changed, 213 insertions, 0 deletions

diff --git a/internal/oidc/claims.go b/internal/oidc/claims.go
new file mode 100644
index 000000000..b58c4662b
--- /dev/null
+++ b/internal/oidc/claims.go
@@ -0,0 +1,27 @@
+/*
+   GoToSocial
+   Copyright (C) 2021 GoToSocial Authors admin@gotosocial.org
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Affero General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Affero General Public License for more details.
+
+   You should have received a copy of the GNU Affero General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+package oidc
+
+// Claims represents claims as found in an id_token returned from an OIDC flow.
+type Claims struct {
+	Email         string   `json:"email"`
+	EmailVerified bool     `json:"email_verified"`
+	Groups        []string `json:"groups"`
+	Name          string   `json:"name"`
+}
diff --git a/internal/oidc/handlecallback.go b/internal/oidc/handlecallback.go
new file mode 100644
index 000000000..2fbdc9309
--- /dev/null
+++ b/internal/oidc/handlecallback.go
@@ -0,0 +1,65 @@
+/*
+   GoToSocial
+   Copyright (C) 2021 GoToSocial Authors admin@gotosocial.org
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Affero General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Affero General Public License for more details.
+
+   You should have received a copy of the GNU Affero General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+package oidc
+
+import (
+	"context"
+	"errors"
+	"fmt"
+)
+
+func (i *idp) HandleCallback(ctx context.Context, code string) (*Claims, error) {
+	l := i.log.WithField("func", "HandleCallback")
+	if code == "" {
+		return nil, errors.New("code was empty string")
+	}
+
+	l.Debug("exchanging code for oauth2token")
+	oauth2Token, err := i.oauth2Config.Exchange(ctx, code)
+	if err != nil {
+		return nil, fmt.Errorf("error exchanging code for oauth2token: %s", err)
+	}
+
+	l.Debug("extracting id_token")
+	rawIDToken, ok := oauth2Token.Extra("id_token").(string)
+	if !ok {
+		return nil, errors.New("no id_token in oauth2token")
+	}
+	l.Debugf("raw id token: %s", rawIDToken)
+
+	// Parse and verify ID Token payload.
+	l.Debug("verifying id_token")
+	idTokenVerifier := i.provider.Verifier(i.oidcConf)
+	idToken, err := idTokenVerifier.Verify(ctx, rawIDToken)
+	if err != nil {
+		return nil, fmt.Errorf("could not verify id token: %s", err)
+	}
+
+	l.Debug("extracting claims from id_token")
+	claims := &Claims{}
+	if err := idToken.Claims(claims); err != nil {
+		return nil, fmt.Errorf("could not parse claims from idToken: %s", err)
+	}
+
+	return claims, nil
+}
+
+func (i *idp) AuthCodeURL(state string) string {
+	return i.oauth2Config.AuthCodeURL(state)
+}
diff --git a/internal/oidc/idp.go b/internal/oidc/idp.go
new file mode 100644
index 000000000..8758f6aad
--- /dev/null
+++ b/internal/oidc/idp.go
@@ -0,0 +1,121 @@
+/*
+   GoToSocial
+   Copyright (C) 2021 GoToSocial Authors admin@gotosocial.org
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Affero General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Affero General Public License for more details.
+
+   You should have received a copy of the GNU Affero General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+package oidc
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/coreos/go-oidc/v3/oidc"
+	"github.com/sirupsen/logrus"
+	"github.com/superseriousbusiness/gotosocial/internal/config"
+	"golang.org/x/oauth2"
+)
+
+const (
+	// CallbackPath is the API path for receiving callback tokens from external OIDC providers
+	CallbackPath = "/auth/callback"
+)
+
+// IDP contains logic for parsing an OIDC access code into a set of claims by calling an external OIDC provider.
+type IDP interface {
+	// HandleCallback accepts a context (pass the context from the http.Request), and an oauth2 code as returned from a successful
+	// login through an OIDC provider. It uses the code to request a token from the OIDC provider, which should contain an id_token
+	// with a set of claims.
+	//
+	// Note that this function *does not* verify state. That should be handled by the caller *before* this function is called.
+	HandleCallback(ctx context.Context, code string) (*Claims, error)
+	// AuthCodeURL returns the proper redirect URL for this IDP, for redirecting requesters to the correct OIDC endpoint.
+	AuthCodeURL(state string) string
+}
+
+type idp struct {
+	oauth2Config oauth2.Config
+	provider     *oidc.Provider
+	oidcConf     *oidc.Config
+	log          *logrus.Logger
+}
+
+// NewIDP returns a new IDP configured with the given config and logger.
+// If the passed config contains a nil value for the OIDCConfig, or OIDCConfig.Enabled
+// is set to false, then nil, nil will be returned. If OIDCConfig.Enabled is true,
+// then the other OIDC config fields must also be set.
+func NewIDP(config *config.Config, log *logrus.Logger) (IDP, error) {
+
+	// oidc isn't enabled so we don't need to do anything
+	if config.OIDCConfig == nil || !config.OIDCConfig.Enabled {
+		return nil, nil
+	}
+
+	// validate config fields
+	if config.OIDCConfig.IDPName == "" {
+		return nil, fmt.Errorf("not set: IDPName")
+	}
+	if config.OIDCConfig.Issuer == "" {
+		return nil, fmt.Errorf("not set: Issuer")
+	}
+	if config.OIDCConfig.ClientID == "" {
+		return nil, fmt.Errorf("not set: ClientID")
+	}
+	if config.OIDCConfig.ClientSecret == "" {
+		return nil, fmt.Errorf("not set: ClientSecret")
+	}
+	if len(config.OIDCConfig.Scopes) == 0 {
+		return nil, fmt.Errorf("not set: Scopes")
+	}
+
+	provider, err := oidc.NewProvider(context.Background(), config.OIDCConfig.Issuer)
+	if err != nil {
+		return nil, err
+	}
+
+	oauth2Config := oauth2.Config{
+		// client_id and client_secret of the client.
+		ClientID:     config.OIDCConfig.ClientID,
+		ClientSecret: config.OIDCConfig.ClientSecret,
+
+		// The redirectURL.
+		RedirectURL: fmt.Sprintf("%s://%s%s", config.Protocol, config.Host, CallbackPath),
+
+		// Discovery returns the OAuth2 endpoints.
+		Endpoint: provider.Endpoint(),
+
+		// "openid" is a required scope for OpenID Connect flows.
+		//
+		// Other scopes, such as "groups" can be requested.
+		Scopes: config.OIDCConfig.Scopes,
+	}
+
+	// create a config for verifier creation
+	oidcConf := &oidc.Config{
+		ClientID: config.OIDCConfig.ClientID,
+	}
+	if config.OIDCConfig.SkipVerification {
+		oidcConf.SkipClientIDCheck = true
+		oidcConf.SkipExpiryCheck = true
+		oidcConf.SkipIssuerCheck = true
+	}
+
+	return &idp{
+		oauth2Config: oauth2Config,
+		oidcConf:     oidcConf,
+		provider:     provider,
+		log:          log,
+	}, nil
+}