Allow coercing a str to a FilePath in MasConfigModel

synapse/config/mas.py

@@ -37,7 +37,8 @@ class MasConfigModel(ParseModel):
     enabled: StrictBool = False
     endpoint: AnyHttpUrl = AnyHttpUrl("http://localhost:8080")
     secret: Optional[StrictStr] = Field(default=None)
-    secret_path: Optional[FilePath] = Field(default=None)
+    # We set `strict=False` to allow `str` instances.
+    secret_path: Optional[FilePath] = Field(default=None, strict=False)
 
     @model_validator(mode="after")
     def verify_secret(self) -> Self:
@@ -69,7 +70,7 @@ class MasConfig(Config):
             parsed = MasConfigModel(**mas_config)
         except ValidationError as e:
             raise ConfigError(
-                "Could not validate Matrix Authentication Service configuration",
+                f"Could not validate Matrix Authentication Service configuration: {e.errors()[0]['msg']}",
                 path=("matrix_authentication_service",),
             ) from e