Should anyone, by accident or on purpose, put a non-metadata file in the metadata file directory, the OIOSAML simply breaks down.
We like to add a README.TXT in the directory to explain it's purpose, and for this we modified SAML20FederationConfig ever so slightly with an added file mask of "*.config":
internal void Initialize()
string[] files = Directory.GetFiles(MetadataLocation, "*.config");
In addition to this, it would be nice if OIOSAML handled non-metadat files by signalling a clear error message, indicating what is wrong.