problem: need to setup upstream auth w/o storing passwords in config

solution: use environment variable placeholders

src/test/groovy/io/emeraldpay/dshackle/config/UpstreamsConfigReaderSpec.groovy

@@ -95,4 +95,26 @@ class UpstreamsConfigReaderSpec extends Specification {
             labels["api"] == "geth"
         }
     }
+
+    def "Post process for usual strings"() {
+        expect:
+        s == reader.postProcess(s)
+        where:
+        s << ["", "a", "13143", "/etc/client1.myservice.com.key", "true", "1a68f20154fc258fe4149c199ad8f281"]
+    }
+
+    def "Post process replaces from env"() {
+        setup:
+        System.setProperty("id", "1")
+        System.setProperty("HOME", "/home/user")
+        System.setProperty("PASSWORD", "1a68f20154fc258fe4149c199ad8f281")
+        expect:
+        replaced == reader.postProcess(orig)
+        where:
+        orig                | replaced
+        "p_\${id}"          | "p_1"
+        "home: \${HOME}"    | "home: /home/user"
+        "\${PASSWORD}"      | "1a68f20154fc258fe4149c199ad8f281"
+    }
+
 }