Add werkzeug ProxyFix X-Forwarded-Prefix support

The base url is not the same as the blueprint mount point because the blueprint url is relative to the application context root.
So either the jinja template needs to be altered to use relative urls, or the base_url should be determined per request.
This commit changes the base_url to url_for(".show"), this makes the UI work for both proxied and direct requests.

Author: sjaek

flask_swagger_ui/flask_swagger_ui.py

@@ -1,6 +1,6 @@
 import os
 import json
-from flask import Blueprint, send_from_directory, render_template, request
+from flask import Blueprint, send_from_directory, render_template, request, url_for
 
 
 def get_swaggerui_blueprint(
@@ -49,7 +49,7 @@ def show(path=None):
                     }
                 )
                 fields["config_json"] = json.dumps(default_config)
-            return render_template("index.template.html", **fields)
+            return render_template("index.template.html", **{**fields, 'base_url': url_for(".show")})
         else:
             return send_from_directory(
                 # A bit of a hack to not pollute the default /static path with our files.