Fix issues in existing client credentials change

This fixes two issues in the existing client credentials change:

- client_credentials was not listed as a supported grant type
- access tokens are not the storage ID

Signed-off-by: Michael Kelly <mkelly@arista.com>

Author: kellyma2

server/handlers.go

@@ -1076,7 +1076,13 @@ func (s *Server) handleClientCredentialsGrant(w http.ResponseWriter, r *http.Req
 
 	claims := storage.Claims{UserID: client.ID}
 
-	accessToken := storage.NewID()
+	accessToken, err := s.newAccessToken(client.ID, claims, scopes, nonce, "client")
+	if err != nil {
+		s.logger.Errorf("failed to create new access token: %v", err)
+		s.tokenErrHelper(w, errServerError, err.Error(), http.StatusInternalServerError)
+		return
+	}
+
 	idToken, expiry, err := s.newIDToken(client.ID, claims, scopes, nonce, accessToken, "", "client")
 	if err != nil {
 		s.tokenErrHelper(w, errServerError, fmt.Sprintf("failed to create ID token: %v", err), http.StatusInternalServerError)

server/server.go

@@ -213,7 +213,7 @@ func newServer(ctx context.Context, c Config, rotationStrategy rotationStrategy)
 		c.SupportedResponseTypes = []string{responseTypeCode}
 	}
 
-	supportedGrant := []string{grantTypeAuthorizationCode, grantTypeRefreshToken, grantTypeDeviceCode} // default
+	supportedGrant := []string{grantTypeAuthorizationCode, grantTypeRefreshToken, grantTypeDeviceCode, grantTypeClientCredentials} // default
 	supportedRes := make(map[string]bool)
 
 	for _, respType := range c.SupportedResponseTypes {