Expand allowedUsers email field to support comma-separated and domains (#9)

* Expand allowedUsers email field to support comma-separated and domains

Closes #8

* Refactor AuthFetch() to return AuthUser struct

Also, this breaks out a parseLine() function which can be easily tested.

* Ignore empty addrs after splitting commas

This ignores a trailing comma

* Add tests for auth parseLine()

* Update documentation in smtprelay.ini

* Fix bug where addrAllowed() was incorrectly case-sensitive

* Update allowedUsers allowed domain format to require leading @

This disambiguates a local user ('john.smith') from a domain ('example.com')

auth_test.go

@@ -0,0 +1,89 @@
+package main
+
+import (
+	"testing"
+)
+
+func stringsEqual(a, b []string) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i, _ := range a {
+		if a[i] != b[i] {
+			return false
+		}
+	}
+	return true
+}
+
+func TestParseLine(t *testing.T) {
+	var tests = []struct {
+		name string
+		expectFail bool
+		line string
+		username string
+		addrs []string
+	}{
+		{
+			name: "Empty line",
+			expectFail: true,
+			line: "",
+		},
+		{
+			name: "Too few fields",
+			expectFail: true,
+			line: "joe",
+		},
+		{
+			name: "Too many fields",
+			expectFail: true,
+			line: "joe xxx joe@example.com whatsthis",
+		},
+		{
+			name: "Normal case",
+			line: "joe xxx joe@example.com",
+			username: "joe",
+			addrs: []string{"joe@example.com"},
+		},
+		{
+			name: "No allowed addrs given",
+			line: "joe xxx",
+			username: "joe",
+			addrs: []string{},
+		},
+		{
+			name: "Trailing comma",
+			line: "joe xxx joe@example.com,",
+			username: "joe",
+			addrs: []string{"joe@example.com"},
+		},
+		{
+			name: "Multiple allowed addrs",
+			line: "joe xxx joe@example.com,@foo.example.com",
+			username: "joe",
+			addrs: []string{"joe@example.com", "@foo.example.com"},
+		},
+	}
+
+	for i, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			user := parseLine(test.line)
+			if user == nil {
+				if !test.expectFail {
+					t.Errorf("parseLine() returned nil unexpectedly")
+				}
+				return
+			}
+
+			if user.username != test.username {
+				t.Errorf("Testcase %d: Incorrect username: expected %v, got %v",
+						 i, test.username, user.username)
+			}
+
+			if !stringsEqual(user.allowedAddresses, test.addrs) {
+				t.Errorf("Testcase %d: Incorrect addresses: expected %v, got %v",
+						 i, test.addrs, user.allowedAddresses)
+			}
+		})
+	}
+}