isinstance for SASL types, so EXTERNAL doesn't have blank user/pass

ircrobots/params.py

@@ -2,23 +2,19 @@ from typing      import Optional
 from dataclasses import dataclass
 
 class SASLParams(object):
-    def __init__(self,
-            mechanism: str,
-            username:  str="",
-            password:  str=""):
-        self.mechanism = mechanism.upper()
-        self.username  = username
-        self.password  = password
+    mechanism: str
 
-class SASLUserPass(SASLParams):
-    def __init__(self, username: str, password: str):
-        super().__init__("USERPASS", username, password)
-class SASLSCRAM(SASLParams):
-    def __init__(self, username: str, password: str):
-        super().__init__("SCRAM", username, password)
+@dataclass
+class _SASLUserPass(SASLParams):
+    username:  str
+    password:  str
+
+class SASLUserPass(_SASLUserPass):
+    mechanism = "USERPASS"
+class SASLSCRAM(_SASLUserPass):
+    mechanism = "SCRAM"
 class SASLExternal(SASLParams):
-    def __init__(self):
-        super().__init__("EXTERNAL")
+    mechanism = "EXTERNAL"
 
 @dataclass
 class STSPolicy(object):

ircrobots/sasl.py

@@ -6,7 +6,7 @@ from ircstates.numerics import *
 
 from .matching import ResponseOr, Responses, Response, ANY
 from .contexts import ServerContext
-from .params   import SASLParams
+from .params   import SASLParams, SASLUserPass, SASLSCRAM, SASLExternal
 from .scram    import SCRAMContext
 
 SASL_SCRAM_MECHANISMS = [
@@ -47,11 +47,11 @@ def _b64db(s: str) -> bytes:
 
 class SASLContext(ServerContext):
     async def from_params(self, params: SASLParams) -> SASLResult:
-        if params.mechanism   == "USERPASS":
+        if isinstance(params, SASLUserPass):
             return await self.userpass(params.username, params.password)
-        elif params.mechanism == "SCRAM":
+        elif isinstance(params, SASLSCRAM):
             return await self.scram(params.username, params.password)
-        elif params.mechanism == "EXTERNAL":
+        elif isinstance(params, SASLExternal):
             return await self.external()
         else:
             raise SASLUnknownMechanismError(