Read existing sssd conf domains and services

Avoid overwriting services and domain sections of system with
an existing sssd.conf (IPA client for example). Copy the
services section used in sssd.conf, and append 'proxy' to
existing domain section.

src/config.jsx

@@ -469,19 +469,54 @@ class SssdConfig extends React.Component {
             superuser: true,
         });
 
+        const conf_syntax_object = {
+            parse:     ini.parse,
+        };
+
+        this.sssdconf = cockpit.file("/etc/sssd/sssd.conf", {
+            syntax: conf_syntax_object,
+            superuser: true,
+        });
+
         const promise = this.file.read();
+        const sssdconfpromise = this.sssdconf.read();
 
         promise.fail(function(error) {
             console.log(error);
         });
+
+        /* It is not an error when the file does not exist, then() callback will
+         * be called with a null value for content and tag is "-" */
+        sssdconfpromise
+                .then((content, tag) => {
+                    if (content !== null) {
+                        this.existingServices = content.sssd.services;
+                        this.existingDomains = content.sssd.domains;
+                    }
+                })
+                .catch(error => {
+                    console.log("Error: " + error);
+                });
     }
 
     handleSubmit(e) {
         const obj = {};
         /* SSSD section */
         obj.sssd = {};
-        obj.sssd.services = "nss";
+        /* Avoid overwriting services and domain sections of existing sssd.conf
-        obj.sssd.domains = "nssfiles";
+         * Copy the services section used in sssd.conf, and append 'proxy' to
+         * existing domain section */
+        if (this.existingServices) {
+            obj.sssd.services = this.existingServices;
+        } else {
+            obj.sssd.services = "nss, pam";
+        }
+
+        if (this.existingDomains) {
+            obj.sssd.domains = this.existingDomains + ", nssfiles";
+        } else {
+            obj.sssd.domains = "nssfiles";
+        }
         /* Proxy provider */
         obj.domainnssfiles = {}; /* Unparser converts this into domain/nssfiles */
         obj.domainnssfiles.id_provider = "proxy";