ENH: Add minimal functionality

Summary

See https://gitlab.indiscale.com/caosdb/customers/lfpb/management/-/issues/381. Review is done in https://gitlab.com/caosdb/caosdb-julialib/-/merge_requests/2

Insert a meaningful description for this merge request here.  What is the
new/changed behavior? Which bug has been fixed? Are there related Issues?

Focus

Point the reviewer to the core of the code change. Where should they start
reading? What should they focus on (e.g. security, performance,
maintainability, user-friendliness, compliance with the specs, finding more
corner cases, concrete questions)?

Test Environment

How to set up a test environment for manual testing?

Check List for the Author

Please, prepare your MR for a review. Be sure to write a summary and a focus and create gitlab comments for the reviewer. They should guide the reviewer through the changes, explain your changes and also point out open questions. For further good practices have a look at our review guidelines

• All automated tests pass
• Reference related Issues
• Up-to-date CHANGELOG.md
• Annotations in code (Gitlab comments)
  • Intent of new code
  • Problems with old code
  • Why this implementation?

Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• Up-to-date CHANGELOG.md
• The test environment setup works and the intended behavior is reproducible in the test environment
• In-code documentation and comments are up-to-date.
• Check: Are there spezifications? Are they satisfied?

For further good practices have a look at our review guidelines.

src/CaosDB.jl

@@ -28,6 +28,44 @@ Chose the name of the library according to the OS you're running.
 """
 library_name = (@static Sys.iswindows() ? "ccaosdb" : "libccaosdb")
 
+module Exceptions
+
+export evaluate_return_code, CaosDBException
+
+using CaosDB
+
+"""
+A generic exception that will be raised in case of non-zero return
+values of the calls to libccaosdb. May carry a message string and a
+code.
+"""
+struct CaosDBException <: Exception
+    msg::String
+    code::Cint
+end
+
+Base.showerror(io::IO, e::CaosDBException) = print(io, "CaosDBException: ", e.msg)
+
+"""
+    function evaluate_return_code(code::Cint)
+
+Evaluate the return code of a libccaosdb ccall and raise a
+`CaosDBException` in case of a non-zero return code.
+"""
+function evaluate_return_code(code::Cint)
+    if code != 0
+        msg = ccall(
+            (:caosdb_get_status_description, CaosDB.library_name),
+            Cstring,
+            (Cint,),
+            code
+        )
+        throw(CaosDBException(unsafe_string(msg), code))
+    end
+end
+
+end # Exceptions
+
 module Info
 
 """
@@ -136,12 +174,8 @@ function create_plain_password_authenticator(
         password,
     )
 
-    if err_code != 0
-
-        @error "Creating authenticator failed with code $err_code"
-
-    end
-
+    CaosDB.Excepions.evaluate_return_code(err_code)
+    
     return auth
 
 end