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package auth
import (
"crypto/rand"
"crypto/sha256"
"encoding/base64"
"encoding/json"
"fmt"
"io"
"net/http"
"net/url"
"strings"
)
type OAuthConfig struct {
ClientID string
RedirectURI string
Scopes []string
}
type OAuthState struct {
State string
CodeVerifier string
DID string
PDS string
AccessToken string
RefreshToken string
KeyPair *DPoPKeyPair
}
type OAuthMetadata struct {
Issuer string `json:"issuer"`
AuthorizationEndpoint string `json:"authorization_endpoint"`
TokenEndpoint string `json:"token_endpoint"`
Scopes []string `json:"scopes_supported"`
}
type TokenResponse struct {
AccessToken string `json:"access_token"`
RefreshToken string `json:"refresh_token"`
TokenType string `json:"token_type"`
ExpiresIn int `json:"expires_in"`
}
func GenerateRandomToken() (string, error) {
b := make([]byte, 32)
_, err := rand.Read(b)
if err != nil {
return "", err
}
return base64.RawURLEncoding.EncodeToString(b), nil
}
func GenerateCodeChallenge(verifier string) string {
h := sha256.Sum256([]byte(verifier))
return base64.URLEncoding.WithPadding(base64.NoPadding).EncodeToString(h[:])
}
func FetchOAuthMetadata(pdsURL string) (*OAuthMetadata, error) {
// first get the resource metadata to find the auth server
resourceURL := fmt.Sprintf("%s/.well-known/oauth-protected-resource", pdsURL)
fmt.Printf("Fetching oauth metadata from: %s\n", resourceURL)
resp, err := http.Get(resourceURL)
if err != nil {
return nil, err
}
defer resp.Body.Close()
var resource struct {
AuthorizationServers []string `json:"authorization_servers"`
}
if err := json.NewDecoder(resp.Body).Decode(&resource); err != nil {
return nil, err
}
if len(resource.AuthorizationServers) == 0 {
return nil, fmt.Errorf("no authorization servers found")
}
// now fetch the actual oauth metadata from the auth server
authServer := resource.AuthorizationServers[0]
metadataURL := fmt.Sprintf("%s/.well-known/oauth-authorization-server", authServer)
resp, err = http.Get(metadataURL)
if err != nil {
return nil, err
}
defer resp.Body.Close()
var metadata OAuthMetadata
if err := json.NewDecoder(resp.Body).Decode(&metadata); err != nil {
return nil, err
}
return &metadata, nil
}
func BuildAuthorizationURL(metadata *OAuthMetadata, config *OAuthConfig, state, codeChallenge, handle string) string {
params := url.Values{
"response_type": {"code"},
"client_id": {config.ClientID},
"redirect_uri": {config.RedirectURI},
"state": {state},
"code_challenge": {codeChallenge},
"code_challenge_method": {"S256"},
"scope": {"atproto"},
"login_hint": {handle},
}
return metadata.AuthorizationEndpoint + "?" + params.Encode()
}
func ExchangeCodeForTokens(pdsURL, code, verifier, backendURL string, keypair *DPoPKeyPair) (*TokenResponse, error) {
metadata, err := FetchOAuthMetadata(pdsURL)
if err != nil {
return nil, err
}
data := url.Values{
"grant_type": {"authorization_code"},
"code": {code},
"redirect_uri": {backendURL + "/api/callback"},
"code_verifier": {verifier},
"client_id": {backendURL + "/api/callback"},
}
fmt.Printf("Sending verifier: %s\n", verifier)
dpopProof, err := keypair.GenerateDPoPProof("POST", metadata.TokenEndpoint, "")
if err != nil {
return nil, err
}
req, err := http.NewRequest("POST", metadata.TokenEndpoint, strings.NewReader(data.Encode()))
if err != nil {
return nil, err
}
req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
req.Header.Set("DPoP", dpopProof)
resp, err := http.DefaultClient.Do(req)
if err != nil {
return nil, err
}
defer resp.Body.Close()
// if nonce required, retry with nonce
if resp.StatusCode == 400 {
body, _ := io.ReadAll(resp.Body)
bodyStr := string(body)
if strings.Contains(bodyStr, "use_dpop_nonce") {
nonce := resp.Header.Get("DPoP-Nonce")
if nonce == "" {
return nil, fmt.Errorf("server requires nonce but didn't provide one")
}
// generate new DPoP proof with nonce
dpopProof, err = keypair.GenerateDPoPProof("POST", metadata.TokenEndpoint, nonce)
if err != nil {
return nil, err
}
retryReq, err := http.NewRequest("POST", metadata.TokenEndpoint, strings.NewReader(data.Encode()))
if err != nil {
return nil, err
}
retryReq.Header.Set("Content-Type", "application/x-www-form-urlencoded")
retryReq.Header.Set("DPoP", dpopProof)
resp, err = http.DefaultClient.Do(retryReq)
if err != nil {
return nil, err
}
defer resp.Body.Close()
} else {
// it's a different 400 error, don't retry
return nil, fmt.Errorf("token exchange failed: 400 - %s", bodyStr)
}
}
if resp.StatusCode != 200 {
body, _ := io.ReadAll(resp.Body)
fmt.Printf("Token exchange error: %s\n", string(body))
return nil, fmt.Errorf("token exchange failed: %d - %s", resp.StatusCode, string(body))
}
var tokens TokenResponse
if err := json.NewDecoder(resp.Body).Decode(&tokens); err != nil {
return nil, err
}
return &tokens, nil
}
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