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//
// Copyright 2024 The Sigstore Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package oauthflow
import (
"context"
"encoding/json"
"fmt"
"io"
"net/http"
"net/url"
"strings"
"time"
"github.com/coreos/go-oidc/v3/oidc"
"golang.org/x/oauth2"
)
// CodeURL fetches the client credentials token authorization endpoint URL from the provider's well-known configuration endpoint
func (d *DefaultFlowClientCredentials) CodeURL() (string, error) {
if d.codeURL != "" {
return d.codeURL, nil
}
wellKnown := strings.TrimSuffix(d.Issuer, "/") + "/.well-known/openid-configuration"
/* #nosec */
httpClient := &http.Client{
Timeout: 3 * time.Second,
}
resp, err := httpClient.Get(wellKnown)
if err != nil {
return "", err
}
defer resp.Body.Close()
body, err := io.ReadAll(resp.Body)
if err != nil {
return "", fmt.Errorf("unable to read response body: %w", err)
}
if resp.StatusCode != http.StatusOK {
return "", fmt.Errorf("%s: %s", resp.Status, body)
}
providerConfig := struct {
Issuer string `json:"issuer"`
TokenEndpoint string `json:"token_endpoint"`
}{}
if err = json.Unmarshal(body, &providerConfig); err != nil {
return "", fmt.Errorf("oidc: failed to decode provider discovery object: %w", err)
}
if d.Issuer != providerConfig.Issuer {
return "", fmt.Errorf("oidc: issuer did not match the issuer returned by provider, expected %q got %q", d.Issuer, providerConfig.Issuer)
}
if providerConfig.TokenEndpoint == "" {
return "", fmt.Errorf("oidc: client credentials token authorization endpoint not returned by provider")
}
d.codeURL = providerConfig.TokenEndpoint
return d.codeURL, nil
}
// DefaultFlowClientCredentials fetches an OIDC Identity token using the Client Credentials Grant flow as specified in RFC8628
type DefaultFlowClientCredentials struct {
Issuer string
codeURL string
}
// NewClientCredentialsFlow creates a new DefaultFlowClientCredentials that retrieves an OIDC Identity Token using a Client Credentials Grant
func NewClientCredentialsFlow(issuer string) *DefaultFlowClientCredentials {
return &DefaultFlowClientCredentials{
Issuer: issuer,
}
}
func (d *DefaultFlowClientCredentials) clientCredentialsFlow(_ *oidc.Provider, clientID, clientSecret, redirectURL string) (string, error) {
data := url.Values{
"client_id": []string{clientID},
"client_secret": []string{clientSecret},
"scope": []string{"openid email"},
"grant_type": []string{"client_credentials"},
}
if redirectURL != "" {
// If a redirect uri is provided then use it
data["redirect_uri"] = []string{redirectURL}
}
codeURL, err := d.CodeURL()
if err != nil {
return "", err
}
/* #nosec */
resp, err := http.PostForm(codeURL, data)
if err != nil {
return "", err
}
defer resp.Body.Close()
b, err := io.ReadAll(resp.Body)
if err != nil {
return "", err
}
if resp.StatusCode != http.StatusOK {
return "", fmt.Errorf("%s: %s", resp.Status, b)
}
tr := tokenResp{}
if err := json.Unmarshal(b, &tr); err != nil {
return "", err
}
if tr.IDToken != "" {
fmt.Println("Token received!")
return tr.IDToken, nil
}
return "", fmt.Errorf("unexpected error in client flow: %s", tr.Error)
}
// GetIDToken gets an OIDC ID Token from the specified provider using the Client Credentials Grant flow
func (d *DefaultFlowClientCredentials) GetIDToken(p *oidc.Provider, cfg oauth2.Config) (*OIDCIDToken, error) {
idToken, err := d.clientCredentialsFlow(p, cfg.ClientID, cfg.ClientSecret, cfg.RedirectURL)
if err != nil {
return nil, err
}
verifier := p.Verifier(&oidc.Config{ClientID: cfg.ClientID})
parsedIDToken, err := verifier.Verify(context.Background(), idToken)
if err != nil {
return nil, err
}
subj, err := SubjectFromToken(parsedIDToken)
if err != nil {
return nil, err
}
return &OIDCIDToken{
RawString: idToken,
Subject: subj,
}, nil
}
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