Username and password in credentials should be optional

[tristan-fitzgerald-vineti]

Describe the bug
In the code segment, these two properties are required, but not needed for a grantType of client_credentials. Making them optional would prevent ide errors that can be misleading.

Expected behavior
If I am using a clientId and clientSecret, I shouldn't need to provide the username or password or avoid type errors by using any as a patch. In testing, the auth works without those two properties being set.

Code Lines

keycloak-nodejs-admin-client/src/utils/auth.ts

Lines 7 to 8 in 1a94e37

	username: string;
	password: string;

Screenshots

It would be great not to need the any above.

[galsilb]

For future reference, using username: null, password: null dose the trick.