Find a string attribute in the builder that has the type attr_type, has a non null value pointer, and is not
invalid in the PKCS#11 sense.
If multiple attributes exist for the given attribute type, then the first one is returned.
| this |
the builder |
| attr_type |
the type of attribute to find |
| value |
the location to place the found value |
|
whether a valid string attribute was found |