Support environment variables in settings.xml file

[hans-kurel]

Currently, the <username> and <password> tags in settings.xml don't support environment variables. When I try using <username>${env.AWS_ACCESS_KEY_ID}</username> for example, the string literal "${env.AWS_ACCESS_KEY_ID}" is sent to AWS. Otherwise, Maven does support environment variables, so would be nice to have this support by this plugin as well.

[jgangemi]

the plugin uses the DefaultCredentialsProvider, so you shouldn't need to specify those environment variables in the settings.xml, they should just be automatically picked up provided they match the expected variable names.