Add support for additional parms for client credentials ktor oauth

Author: mpgxvii

radar-commons-kotlin/src/main/kotlin/org/radarbase/ktor/auth/ClientCredentialsConfig.kt

@@ -6,6 +6,7 @@ data class ClientCredentialsConfig(
     val tokenUrl: String,
     val clientId: String? = null,
     val clientSecret: String? = null,
+    val additionalParameters: Map<String, String>? = null,
 ) {
     /**
      * Fill in the client ID and client secret from environment variables. The variables are

radar-commons-kotlin/src/main/kotlin/org/radarbase/ktor/auth/OAuthClientProvider.kt

@@ -56,6 +56,9 @@ fun Auth.clientCredentials(
                     append("grant_type", "client_credentials")
                     append("client_id", authConfig.clientId)
                     append("client_secret", authConfig.clientSecret)
+                    authConfig.additionalParameters?.forEach { (key, value) ->
+                        append(key, value)
+                    }
                 },
             ) {
                 accept(ContentType.Application.Json)