Implement fmt.Stringer on rest.Config to sanitize sensitive fields

It's very easy to add glog.Info(config) calls for debugging (or actual
logging). In some scenarios those configs will carry sensitive tokens
and those tokens will end up in logs or response bodies.
Leaking of those stringified configs compromises the cluster.

Also implement fmt.GoStringer.

Kubernetes-commit: c9ad1d7339b164dfba0846ec49fa4a52474d3e23

rest/config.go

@@ -129,6 +129,47 @@ type Config struct {
 	// Version string
 }
 
+var _ fmt.Stringer = new(Config)
+var _ fmt.GoStringer = new(Config)
+
+type sanitizedConfig *Config
+
+type sanitizedAuthConfigPersister struct{ AuthProviderConfigPersister }
+
+func (sanitizedAuthConfigPersister) GoString() string {
+	return "rest.AuthProviderConfigPersister(--- REDACTED ---)"
+}
+func (sanitizedAuthConfigPersister) String() string {
+	return "rest.AuthProviderConfigPersister(--- REDACTED ---)"
+}
+
+// GoString implements fmt.GoStringer and sanitizes sensitive fields of Config
+// to prevent accidental leaking via logs.
+func (c *Config) GoString() string {
+	return c.String()
+}
+
+// String implements fmt.Stringer and sanitizes sensitive fields of Config to
+// prevent accidental leaking via logs.
+func (c *Config) String() string {
+	if c == nil {
+		return "<nil>"
+	}
+	cc := sanitizedConfig(CopyConfig(c))
+	// Explicitly mark non-empty credential fields as redacted.
+	if cc.Password != "" {
+		cc.Password = "--- REDACTED ---"
+	}
+	if cc.BearerToken != "" {
+		cc.BearerToken = "--- REDACTED ---"
+	}
+	if cc.AuthConfigPersister != nil {
+		cc.AuthConfigPersister = sanitizedAuthConfigPersister{cc.AuthConfigPersister}
+	}
+
+	return fmt.Sprintf("%#v", cc)
+}
+
 // ImpersonationConfig has all the available impersonation options
 type ImpersonationConfig struct {
 	// UserName is the username to impersonate on each request.
@@ -168,6 +209,40 @@ type TLSClientConfig struct {
 	CAData []byte
 }
 
+var _ fmt.Stringer = TLSClientConfig{}
+var _ fmt.GoStringer = TLSClientConfig{}
+
+type sanitizedTLSClientConfig TLSClientConfig
+
+// GoString implements fmt.GoStringer and sanitizes sensitive fields of
+// TLSClientConfig to prevent accidental leaking via logs.
+func (c TLSClientConfig) GoString() string {
+	return c.String()
+}
+
+// String implements fmt.Stringer and sanitizes sensitive fields of
+// TLSClientConfig to prevent accidental leaking via logs.
+func (c TLSClientConfig) String() string {
+	cc := sanitizedTLSClientConfig{
+		Insecure:   c.Insecure,
+		ServerName: c.ServerName,
+		CertFile:   c.CertFile,
+		KeyFile:    c.KeyFile,
+		CAFile:     c.CAFile,
+		CertData:   c.CertData,
+		KeyData:    c.KeyData,
+		CAData:     c.CAData,
+	}
+	// Explicitly mark non-empty credential fields as redacted.
+	if len(cc.CertData) != 0 {
+		cc.CertData = []byte("--- TRUNCATED ---")
+	}
+	if len(cc.KeyData) != 0 {
+		cc.KeyData = []byte("--- REDACTED ---")
+	}
+	return fmt.Sprintf("%#v", cc)
+}
+
 type ContentConfig struct {
 	// AcceptContentTypes specifies the types the client will accept and is optional.
 	// If not set, ContentType will be used to define the Accept header