oauth: add minimal device auth support for ssh (#5657)

## Summary

This adds the necessary logic needed for device auth flow in ssh. The
code is not used currently; will follow up with testenv updates that can
let us test this with the mock idp.

## Related issues

<!-- For example...
- #159
-->

## User Explanation

<!-- How would you explain this change to the user? If this
change doesn't create any user-facing changes, you can leave
this blank. If filled out, add the `docs` label -->

## Checklist

- [ ] reference any related issues
- [ ] updated unit tests
- [ ] add appropriate label (`enhancement`, `bug`, `breaking`,
`dependencies`, `ci`)
- [ ] ready for review

pkg/identity/mock_provider.go

@@ -20,6 +20,10 @@ type MockProvider struct {
 	UpdateUserInfoError       error
 	SignInError               error
 	SignOutError              error
+	DeviceAuthResponse        oauth2.DeviceAuthResponse
+	DeviceAuthError           error
+	DeviceAccessTokenResponse oauth2.Token
+	DeviceAccessTokenError    error
 }
 
 // Authenticate is a mocked providers function.
@@ -57,6 +61,16 @@ func (mp MockProvider) SignIn(_ http.ResponseWriter, _ *http.Request, _ string)
 	return mp.SignInError
 }
 
+// DeviceAuth implements Authenticator.
+func (mp MockProvider) DeviceAuth(_ context.Context) (*oauth2.DeviceAuthResponse, error) {
+	return &mp.DeviceAuthResponse, mp.DeviceAuthError
+}
+
+// DeviceAccessToken implements Authenticator.
+func (mp MockProvider) DeviceAccessToken(_ context.Context, _ *oauth2.DeviceAuthResponse, _ identity.State) (*oauth2.Token, error) {
+	return &mp.DeviceAccessTokenResponse, mp.DeviceAccessTokenError
+}
+
 // VerifyAccessToken verifies an access token.
 func (mp MockProvider) VerifyAccessToken(_ context.Context, _ string) (claims map[string]any, err error) {
 	return nil, fmt.Errorf("VerifyAccessToken not implemented")

pkg/identity/oauth/apple/apple.go

@@ -188,6 +188,14 @@ func (p *Provider) SignOut(_ http.ResponseWriter, _ *http.Request, _, _, _ strin
 	return oidc.ErrSignoutNotImplemented
 }
 
+func (p *Provider) DeviceAuth(_ context.Context) (*oauth2.DeviceAuthResponse, error) {
+	return nil, oidc.ErrDeviceAuthNotImplemented
+}
+
+func (p *Provider) DeviceAccessToken(_ context.Context, _ *oauth2.DeviceAuthResponse, _ identity.State) (*oauth2.Token, error) {
+	return nil, oidc.ErrDeviceAuthNotImplemented
+}
+
 // VerifyAccessToken verifies an access token.
 func (p *Provider) VerifyAccessToken(_ context.Context, _ string) (claims map[string]any, err error) {
 	// apple does not appear to have any way of verifying access tokens

pkg/identity/oauth/github/github.go

@@ -258,6 +258,14 @@ func (p *Provider) SignOut(_ http.ResponseWriter, _ *http.Request, _, _, _ strin
 	return oidc.ErrSignoutNotImplemented
 }
 
+func (p *Provider) DeviceAuth(_ context.Context) (*oauth2.DeviceAuthResponse, error) {
+	return nil, oidc.ErrDeviceAuthNotImplemented
+}
+
+func (p *Provider) DeviceAccessToken(_ context.Context, _ *oauth2.DeviceAuthResponse, _ identity.State) (*oauth2.Token, error) {
+	return nil, oidc.ErrDeviceAuthNotImplemented
+}
+
 // VerifyAccessToken verifies an access token.
 func (p *Provider) VerifyAccessToken(ctx context.Context, rawAccessToken string) (claims map[string]any, err error) {
 	claims = jwtutil.Claims(map[string]any{})

pkg/identity/oidc/errors.go

@@ -13,6 +13,10 @@ var ErrRevokeNotImplemented = errors.New("identity/oidc: revoke not implemented"
 // https://openid.net/specs/openid-connect-frontchannel-1_0.html#RPInitiated
 var ErrSignoutNotImplemented = errors.New("identity/oidc: end session not implemented")
 
+// ErrDeviceAuthNotImplemented is returned when device auth is not implemented
+// by an identity provider.
+var ErrDeviceAuthNotImplemented = errors.New("identity/oidc: device auth not implemented")
+
 // ErrMissingProviderURL is returned when an identity provider requires a provider url
 // does not receive one.
 var ErrMissingProviderURL = errors.New("identity/oidc: missing provider url")

pkg/identity/oidc/oidc.go

@@ -133,11 +133,30 @@ func (p *Provider) SignIn(w http.ResponseWriter, r *http.Request, state string)
 func (p *Provider) Authenticate(ctx context.Context, code string, v identity.State) (*oauth2.Token, error) {
 	ctx, span := trace.Continue(ctx, "oidc: authenticate")
 	defer span.End()
+	token, err := p.authenticate(ctx, v, func(oa *oauth2.Config) (*oauth2.Token, error) {
+		return p.exchange(ctx, code, oa)
+	})
+	if err != nil {
+		span.SetStatus(codes.Error, err.Error())
+		return nil, err
+	}
+	return token, nil
+}
 
-	oauth2Token, idToken, err := p.exchange(ctx, code)
+func (p *Provider) authenticate(ctx context.Context, v identity.State, exchange func(oa *oauth2.Config) (*oauth2.Token, error)) (*oauth2.Token, error) {
+	oa, err := p.GetOauthConfig()
 	if err != nil {
 		return nil, err
 	}
+	oauth2Token, err := exchange(oa)
+	if err != nil {
+		return nil, err
+	}
+
+	idToken, err := p.getIDToken(ctx, oauth2Token)
+	if err != nil {
+		return nil, fmt.Errorf("identity/oidc: failed getting id_token: %w", err)
+	}
 
 	if rawIDToken, ok := oauth2Token.Extra("id_token").(string); ok {
 		v.SetRawIDToken(rawIDToken)
@@ -146,46 +165,29 @@ func (p *Provider) Authenticate(ctx context.Context, code string, v identity.Sta
 	// hydrate `v` using claims inside the returned `id_token`
 	// https://openid.net/specs/openid-connect-core-1_0.html#TokenEndpoint
 	if err := idToken.Claims(v); err != nil {
-		err := fmt.Errorf("identity/oidc: couldn't unmarshal extra claims %w", err)
-		span.SetStatus(codes.Error, err.Error())
-		return nil, err
+		return nil, fmt.Errorf("identity/oidc: couldn't unmarshal extra claims %w", err)
 	}
 
 	if err := p.UpdateUserInfo(ctx, oauth2Token, v); err != nil {
-		err := fmt.Errorf("identity/oidc: couldn't update user info %w", err)
-		span.SetStatus(codes.Error, err.Error())
-		return nil, err
+		return nil, fmt.Errorf("identity/oidc: couldn't update user info %w", err)
 	}
 
 	return oauth2Token, nil
 }
 
-func (p *Provider) exchange(ctx context.Context, code string) (*oauth2.Token, *go_oidc.IDToken, error) {
+func (p *Provider) exchange(ctx context.Context, code string, oa *oauth2.Config) (*oauth2.Token, error) {
 	ctx, span := trace.Continue(ctx, "oidc: token exchange")
 	defer span.End()
 
-	oa, err := p.GetOauthConfig()
-	if err != nil {
-		span.SetStatus(codes.Error, err.Error())
-		return nil, nil, err
-	}
-
 	// Exchange converts an authorization code into a token.
 	oauth2Token, err := oa.Exchange(ctx, code)
 	if err != nil {
 		err := fmt.Errorf("identity/oidc: token exchange failed: %w", err)
 		span.SetStatus(codes.Error, err.Error())
-		return nil, nil, err
+		return nil, err
 	}
 
-	idToken, err := p.getIDToken(ctx, oauth2Token)
-	if err != nil {
-		err := fmt.Errorf("identity/oidc: failed getting id_token: %w", err)
-		span.SetStatus(codes.Error, err.Error())
-		return nil, nil, err
-	}
-
-	return oauth2Token, idToken, nil
+	return oauth2Token, nil
 }
 
 // UpdateUserInfo calls the OIDC (spec required) UserInfo Endpoint as well as any
@@ -366,6 +368,40 @@ func (p *Provider) SignOut(w http.ResponseWriter, r *http.Request, idTokenHint,
 	return nil
 }
 
+func (p *Provider) DeviceAuth(ctx context.Context) (*oauth2.DeviceAuthResponse, error) {
+	ctx, span := trace.Continue(ctx, "oidc: DeviceAuth")
+	defer span.End()
+
+	oa, err := p.GetOauthConfig()
+	if err != nil {
+		return nil, err
+	}
+
+	opts := defaultAuthCodeOptions
+	for k, v := range p.AuthCodeOptions {
+		opts = append(opts, oauth2.SetAuthURLParam(k, v))
+	}
+
+	resp, err := oa.DeviceAuth(ctx, opts...)
+	if err != nil {
+		return nil, err
+	}
+	return resp, nil
+}
+
+func (p *Provider) DeviceAccessToken(ctx context.Context, da *oauth2.DeviceAuthResponse, v identity.State) (*oauth2.Token, error) {
+	ctx, span := trace.Continue(ctx, "oidc: DeviceAccessToken")
+	defer span.End()
+	token, err := p.authenticate(ctx, v, func(oa *oauth2.Config) (*oauth2.Token, error) {
+		return oa.DeviceAccessToken(ctx, da)
+	})
+	if err != nil {
+		span.SetStatus(codes.Error, err.Error())
+		return nil, err
+	}
+	return token, nil
+}
+
 // VerifyAccessToken verifies an access token.
 func (p *Provider) VerifyAccessToken(ctx context.Context, rawAccessToken string) (claims map[string]any, err error) {
 	pp, err := p.GetProvider()

pkg/identity/providers.go

@@ -41,6 +41,9 @@ type Authenticator interface {
 
 	SignIn(w http.ResponseWriter, r *http.Request, state string) error
 	SignOut(w http.ResponseWriter, r *http.Request, idTokenHint, authenticateSignedOutURL, redirectToURL string) error
+
+	DeviceAuth(ctx context.Context) (*oauth2.DeviceAuthResponse, error)
+	DeviceAccessToken(ctx context.Context, r *oauth2.DeviceAuthResponse, state State) (*oauth2.Token, error)
 }
 
 // AuthenticatorConstructor makes an Authenticator from the given options.