/usr/share/accounts/providers/facebook.provider is in account-plugin-facebook 0.12+16.04.20160126-0ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 | <?xml version="1.0" encoding="UTF-8"?>
<provider id="facebook">
  <name>Facebook</name>
  <icon>facebook</icon>
  <translations>account-plugins</translations>
  <domains>.*facebook\.com</domains>
  <plugin>generic-oauth</plugin>
  <single-account>true</single-account>
  <template>
    <group name="auth">
      <setting name="method">oauth2</setting>
      <setting name="mechanism">user_agent</setting>
      <group name="oauth2">
        <group name="user_agent">
          <setting name="Host">www.facebook.com</setting>
          <setting name="AuthPath">/dialog/oauth</setting>
          <setting name="RedirectUri">https://www.facebook.com/connect/login_success.html</setting>
          <setting name="ResponseType">token</setting>
          <setting name="Display">popup</setting>
          <setting type="as" name="Scope">['publish_actions','user_photos']</setting>
          <setting name="ClientId">271112146382618</setting>
          <setting type="as" name="AllowedSchemes">['https','http']</setting>
        </group>
      </group>
    </group>
  </template>
</provider>
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