FEATURE: Allow JSON paths with literal dots in the keys (#33)

This is achieved by surrounding a key with double quotes, or by escaping
the dot character with a backslash.

For example, given the JSON

```
{ "www.example.com/uid": "myuid" }
```

Previously, there was no way to access this value. The dots would make
the parser try to access `json["www"]["example"]["com/uid"]`.

Now, this value can be accessed by using a `oauth2_json_user_id_path` like:

```
www\.example\.com/uid
```
or alternatively:
```
"www.example.com/uid"
```

plugin.rb

@@ -166,12 +166,34 @@ class ::OAuth2BasicAuthenticator < Auth::ManagedAuthenticator
     if path.present?
       #this.[].that is the same as this.that, allows for both this[0].that and this.[0].that path styles
       path = path.gsub(".[].", ".").gsub(".[", "[")
-      segments = path.split('.')
+      segments = parse_segments(path)
       val = walk_path(user_json, segments)
       result[prop] = val if val.present?
     end
   end
 
+  def parse_segments(path)
+    segments = [+""]
+    quoted = false
+    escaped = false
+
+    path.split("").each do |char|
+      next_char_escaped = false
+      if !escaped && (char == '"')
+        quoted = !quoted
+      elsif !escaped && !quoted && (char == '.')
+        segments.append +""
+      elsif !escaped && (char == '\\')
+        next_char_escaped = true
+      else
+        segments.last << char
+      end
+      escaped = next_char_escaped
+    end
+
+    segments
+  end
+
   def log(info)
     Rails.logger.warn("OAuth2 Debugging: #{info}") if SiteSetting.oauth2_debug_auth
   end

spec/plugin_spec.rb

@@ -177,6 +177,38 @@ describe OAuth2BasicAuthenticator do
     expect(result).to eq "test@example.com"
   end
 
+  it 'allows keys containing dots, if wrapped in quotes' do
+    authenticator = OAuth2BasicAuthenticator.new
+    json_string = '{"www.example.com/uid": "myuid"}'
+    SiteSetting.oauth2_json_user_id_path = '"www.example.com/uid"'
+    result = authenticator.json_walk({}, JSON.parse(json_string), :user_id)
+
+    expect(result).to eq "myuid"
+  end
+
+  it 'allows keys containing dots, if escaped' do
+    authenticator = OAuth2BasicAuthenticator.new
+    json_string = '{"www.example.com/uid": "myuid"}'
+    SiteSetting.oauth2_json_user_id_path = 'www\.example\.com/uid'
+    result = authenticator.json_walk({}, JSON.parse(json_string), :user_id)
+
+    expect(result).to eq "myuid"
+  end
+
+  it 'allows keys containing literal backslashes, if escaped' do
+    authenticator = OAuth2BasicAuthenticator.new
+    # This 'single quoted heredoc' syntax means we don't have to escape backslashes in Ruby
+    # What you see is exactly what the user would enter in the site settings
+    json_string = <<~'_'.chomp
+      {"www.example.com/uid\\": "myuid"}
+    _
+    SiteSetting.oauth2_json_user_id_path = <<~'_'.chomp
+      www\.example\.com/uid\\
+    _
+    result = authenticator.json_walk({}, JSON.parse(json_string), :user_id)
+    expect(result).to eq "myuid"
+  end
+
   it 'can walk json that contains an array' do
     authenticator = OAuth2BasicAuthenticator.new
     json_string = '{"email":"test@example.com","identities":[{"user_id":"123456789","provider":"auth0","isSocial":false}]}'