Since 2.3.25, do it like this:
<#list user as propName, propValue>
${propName} = ${propValue}
</#list>
Note that this also works with non-string keys (unlike map[key], which had to be written as map?api.get(key) then).
Before 2.3.25 the standard solution was:
<#list user?keys as prop>
${prop} = ${user[prop]}
</#list>
However, some really old FreeMarker integrations use a strange configuration, where the public Map methods (like getClass) appear as keys. That happens as they are using a pure BeansWrapper (instead of DefaultObjectWrapper) whose simpleMapWrapper property was left on false. You should avoid such a setup, as it mixes the methods with real Map entries. But if you run into such unfortunate setup, the way to escape the situation is using the exposed Java methods, such as user.entrySet(), user.get(key), etc., and not using the template language constructs like ?keys or user[key].