refactor: avoid dynamic call

apps/emqx_dashboard_sso/src/emqx_dashboard_sso_api.erl

@@ -239,7 +239,7 @@ sp_saml_metadata(get, _Req) ->
         undefined ->
             {404, ?BACKEND_NOT_FOUND, <<"Backend not found">>};
         #{sp := SP} = _State ->
-            SignedXml = SP:generate_metadata(),
+            SignedXml = esaml_sp:generate_metadata(SP),
             Metadata = xmerl:export([SignedXml], xmerl_xml),
             {200, [{<<"Content-Type">>, <<"text/xml">>}], Metadata}
     end.

apps/emqx_dashboard_sso/src/emqx_dashboard_sso_saml.erl

@@ -129,7 +129,7 @@ destroy(#{resource_id := ResourceId}) ->
     ok.
 
 login(_Req, #{sp := SP, idp_meta := #esaml_idp_metadata{login_location = IDP}} = _State) ->
-    SignedXml = SP:generate_authn_request(IDP),
+    SignedXml = esaml_sp:generate_authn_request(IDP, SP),
     Target = esaml_binding:encode_http_redirect(IDP, SignedXml, <<>>),
     %% TODO: _Req acutally is HTTP request body, not fully request
     RedirectFun = fun(Headers) ->