crypto/src/main/java/org/springframework/security/crypto/password/MessageDigestPasswordEncoder.java
public boolean matches(CharSequence rawPassword, String encodedPassword) {
		String salt = extractSalt(encodedPassword);
		String rawPasswordEncoded = digest(salt, rawPassword);
		return PasswordEncoderUtils.equals(encodedPassword.toString(), rawPasswordEncoded);
	}
public boolean matches(CharSequence rawPassword, String encodedPassword) {
		String salt = extractSalt(encodedPassword);
		String rawPasswordEncoded = digest(salt, rawPassword);
		return PasswordEncoderUtils.equals(encodedPassword.toString(), rawPasswordEncoded);
	}
Takes a previously encoded password and compares it with a rawpassword after mixing
in the salt and encoding that value

@param rawPassword plain text password
@param encodedPassword previously encoded password
@return true or false