toEncode.Auth = encodeDockerConfigFieldAuth(ident.Username, ident.Password)

	return json.Marshal(toEncode)
}

// decodeDockerConfigFieldAuth deserializes the "auth" field from dockercfg into a
// username and a password. The format of the auth field is base64(<username>:<password>).
func decodeDockerConfigFieldAuth(field string) (username, password string, err error) {

	var decoded []byte

	// StdEncoding can only decode padded string

			input: "Zm9vOmJhcg== ",
			fail:  true,
		},

		// bad base64 data
		{
			input: "pants",
			fail:  true,
		},
	}

	for i, tt := range tests {
		username, password, err := decodeDockerConfigFieldAuth(tt.input)
		if (err != nil) != tt.fail {
			t.Errorf("case %d: expected fail=%t, got err=%v", i, tt.fail, err)
		}

		if tt.username != username {