Add custom rich_text template filter

src/pretix/base/templatetags/rich_text.py

@@ -0,0 +1,45 @@
+import bleach
+import markdown
+from django import template
+from django.utils.safestring import mark_safe
+
+register = template.Library()
+
+ALLOWED_TAGS = [
+    'a',
+    'abbr',
+    'acronym',
+    'b',
+    'blockquote',
+    'code',
+    'em',
+    'i',
+    'li',
+    'ol',
+    'strong',
+    'ul',
+    'p',
+    'table',
+    'tbody',
+    'thead',
+    'tr',
+    'td',
+    'th',
+]
+
+ALLOWED_ATTRIBUTES = {
+    'a': ['href', 'title'],
+    'abbr': ['title'],
+    'acronym': ['title'],
+    'table': ['width'],
+    'td': ['width', 'align'],
+}
+
+
+@register.filter
+def rich_text(text: str, **kwargs):
+    """
+    Processes markdown and cleans HTML in a text input.
+    """
+    body_md = bleach.linkify(bleach.clean(markdown.markdown(text), tags=ALLOWED_TAGS, attributes=ALLOWED_ATTRIBUTES))
+    return mark_safe(body_md)