user-id maven plugin
This  plugin provides the user-id (UID) of the user executing the build.
Due  to  the java system itself not providing this information but  only
the  username,  the plugin gets the property user.name of the  systems
properties.  This  unfortunately  breaky  the possibillity  to  use  the
plugin for non-standard unix-environments.
WARNING
Using  this plugin could couple your build tightly to your  environment.
Please use it only if you really need it.
Example
To enable the plugin add this to your build-plugins in your pom.xml.
<plugin>
  <!-- Plugin only works with unix-like environments, please use it wisely! -->
  <groupId>org.rjung.util</groupId>
  <artifactId>user-id-maven-plugin</artifactId>
  <version>1.0</version>
  <!-- (If you have an idea how I can omit the executions, please contact the author of this plugin) -->
  <executions>
    <execution>
      <goals>
        <goal>user-id</goal>
      </goals>
    </execution>
  </executions>
</plugin>
Now you can use ${user.id} within your pom.xml.
Configuration
You can adapt some different values to your need:
<plugin>
  <!-- Plugin only works with unix-like environments, please use it wisely! -->
  <!-- This contains the default configuration for standard unix systems. -->
  <groupId>org.rjung.util</groupId>
  <artifactId>user-id-maven-plugin</artifactId>
  <version>1.0</version>
  <configuration>
    <propertyName>user.id</propertyName>
    <passwdPath>/etc/passwd</passwdPath>
    <columnSeparator>:</columnSeparator>
    <usernameColumn>0</usernameColumn><!-- first column is 0 -->
    <uidColumn>2</uidColumn>
    <defaultUid>0</defaultUid>
  </configuration>
  <!-- (If you have an idea how I can omit the executions, please contact the author of this plugin) -->
  <executions>
    <execution>
      <goals>
        <goal>user-id</goal>
      </goals>
    </execution>
  </executions>
</plugin>