Common tls (#474)

* Add common TLS config routines

These routines can be used to load TLS configs based upon the
args in the Corefile.

* Add common routine for Corefile arg handling

Add the NewTLSConfigFromArgs routine so that you can just pass
in the Corefile args and get a tls.Config. This ensures the
parameters are handled consistently across middleware.

* Change to varargs style params

Change to use args ...string instead of []string. Add
documentation of what each call means.

middleware/test/file.go

@@ -3,6 +3,7 @@ package test
 import (
 	"io/ioutil"
 	"os"
+	"path/filepath"
 )
 
 // TempFile will create a temporary file on disk and returns the name and a cleanup function to remove it later.
@@ -17,3 +18,90 @@ func TempFile(dir, content string) (string, func(), error) {
 	rmFunc := func() { os.Remove(f.Name()) }
 	return f.Name(), rmFunc, nil
 }
+
+// WritePEMFiles creates a tmp dir with ca.pem, cert.pem, and key.pem and the func to remove it
+func WritePEMFiles(dir string) (string, func(), error) {
+	tempDir, err := ioutil.TempDir(dir, "go-test-pemfiles")
+	if err != nil {
+		return "", nil, err
+	}
+
+	data := `-----BEGIN CERTIFICATE-----
+MIIC9zCCAd+gAwIBAgIJALGtqdMzpDemMA0GCSqGSIb3DQEBCwUAMBIxEDAOBgNV
+BAMMB2t1YmUtY2EwHhcNMTYxMDE5MTU1NDI0WhcNNDQwMzA2MTU1NDI0WjASMRAw
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+I1rs/VUGKzcJGVIWbHrgjP68CTStGAvKgbsTqw7aLXTSqtPw88N9XVSyRg==
+-----END CERTIFICATE-----`
+	path := filepath.Join(tempDir, "ca.pem")
+	if err := ioutil.WriteFile(path, []byte(data), 0644); err != nil {
+		return "", nil, err
+	}
+	data = `-----BEGIN CERTIFICATE-----
+MIICozCCAYsCCQCRlf5BrvPuqjANBgkqhkiG9w0BAQsFADASMRAwDgYDVQQDDAdr
+dWJlLWNhMB4XDTE2MTAxOTE2MDUxOFoXDTE3MTAxOTE2MDUxOFowFTETMBEGA1UE
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+qeg10RdFnw==
+-----END CERTIFICATE-----`
+	path = filepath.Join(tempDir, "cert.pem")
+	if err = ioutil.WriteFile(path, []byte(data), 0644); err != nil {
+		return "", nil, err
+	}
+
+	data = `-----BEGIN RSA PRIVATE KEY-----
+MIIEpgIBAAKCAQEAxPBrvAIWiIJp383ndpRF+OuZ74pHsVLTJ/lSv05H+gzcGhL2
+y1i7kWXOvfmgvlPq3kZzZ7LvyZSz8KzTumyeNR0ofnlsOklJ0bvNb2Zc3J4vAh58
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+8chzqtkH6b2b2R73hyRysWjsomys34ma3mEEPTX/aXeAF2MSZ/EWT9yL
+-----END RSA PRIVATE KEY-----`
+	path = filepath.Join(tempDir, "key.pem")
+	if err = ioutil.WriteFile(path, []byte(data), 0644); err != nil {
+		return "", nil, err
+	}
+
+	rmFunc := func() { os.RemoveAll(tempDir) }
+	return tempDir, rmFunc, nil
+}