java.util.Properties should also be supported. With this, one jndi property would be enough to configure logback, with variable substitution, like:

<insertFromJNDI env-entry-name="myRes" as="res" /> <!-- {dir=myDir} -->
<appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
    <file>${res.dir}/myLog.log</file>
...
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