Could not get unknown property 'mavenUser' for Credentials

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2

Th answer is already in your commented line.

// ~/.gradle/gradle.properties should be configured!
            credentials {
                username mavenUser
                password mavenPassword
            }
            url 'http://dev.softwerk.se:8080/nexus/content/repositories/softwerk-repo'

Edit or create ~/.gradle/gradle.properties if not exist yet.
Then add

mavenUser=yourusername
mavenPassword=secretpassword

The yourusername and secretpassword are to be provided from the maven repo dev.softwerk.se