feat(authentication): provide an authentication mechanism (#19)

* moves server into session

* renames jsonrpc server to jsonrpc proxy

* moves server into session

* renames jsonrpc server to jsonrpc proxy

* adds json rpc server

* removes obsolete proxy from protocol

* changes interface of jsonrpc_proxy_onresult to accept previously parsed messages

* adds infrastructure to process incoming requests; fixes invalid read of ill formatted responses

* adds description of authentication request

* adds authentication request

* adds userdb for authentication purposes

* removes debug code: console.log()

* fixes cmake build error (missing openssl symbols)

* fixes typo

* replaces ASCII art by UML diagram

* renames BAD_NOACCESS to BAD_ACCESS_DENIED

* fixes style

* adds docu of authentication

* ignored false positives of flawfinder

* fixes style issues

* fixes javascript style issues

doc/authenticate.uml

@@ -0,0 +1,28 @@
+@startuml
+participant "Filesystem Provider\n(e.g. Webbrowser)" as provider
+participant "webfuse\ndaemon" as daemon
+actor "user" as user
+
+group directory listing fails without authentication
+user     -> daemon : ls
+daemon   -> daemon : is_authenticated
+daemon   -->x user : error: no entry
+end
+
+
+group authenticate
+provider -> daemon: authenticate(type, credentials)
+daemon -> daemon: get_authenticator(type)
+daemon -> daemon: check(credentials)
+daemon --> provider: result
+end
+
+group directory listing succeeds after authentication
+user     -> daemon : ls
+daemon   -> daemon : is_authenticated
+daemon   -> provider : readdir
+provider --> daemon : readdir_resp
+daemon   --> user : [., ..]
+end
+
+@enduml

doc/concept.uml

@@ -0,0 +1,30 @@
+@startuml
+participant "Filesystem Provider\n(e.g. Webbrowser)" as provider
+participant "webfuse\ndaemon" as daemon
+actor "user" as user
+
+group startup
+daemon -> daemon : fuse_mount
+daemon -> daemon : start ws
+end
+...
+
+group connect
+provider -> daemon : connect
+    opt authentication
+    provider -> daemon: authenticate
+    daemon -> daemon: check credentials
+    daemon --> provider: okay
+    end
+end
+...
+
+group directory listing
+user     -> daemon : ls
+daemon   -> provider : readdir
+provider --> daemon : readdir_resp
+daemon   --> user : [., ..]
+end
+...
+
+@enduml