fix: wrong client app registration endpoint

POST /api/v2/oauth2-provider/apps is actually for manual admin
registration for admin created apps. Programmatic Dynamic Client
Registration is done via `POST /oauth2/register`.

At the same time I included `registration_access_token` and `registration_client_uri`
to use it later in order to refresh the client secret without re-registering the client app.

Author: fioan89

src/main/kotlin/com/coder/toolbox/oauth/ClientRegistrationResponse.kt

@@ -17,5 +17,7 @@ data class ClientRegistrationResponse(
     @field:Json(name = "scope") val scope: String,
     @field:Json(name = "token_endpoint_auth_method") val tokenEndpointAuthMethod: String,
     @field:Json(name = "client_id_issued_at") val clientIdIssuedAt: Long?,
-    @field:Json(name = "client_secret_expires_at") val clientSecretExpiresAt: Long?
+    @field:Json(name = "client_secret_expires_at") val clientSecretExpiresAt: Long?,
+    @field:Json(name = "registration_client_uri") val registrationClientUri: String,
+    @field:Json(name = "registration_access_token") val registrationAccessToken: String
 )

src/main/kotlin/com/coder/toolbox/oauth/CoderAuthorizationApi.kt

@@ -4,15 +4,13 @@ import retrofit2.Response
 import retrofit2.http.Body
 import retrofit2.http.GET
 import retrofit2.http.POST
-import retrofit2.http.Url
 
 interface CoderAuthorizationApi {
     @GET(".well-known/oauth-authorization-server")
     suspend fun discoveryMetadata(): Response<AuthorizationServer>
 
-    @POST
+    @POST("oauth2/register")
     suspend fun registerClient(
-        @Url url: String,
         @Body request: ClientRegistrationRequest
     ): Response<ClientRegistrationResponse>
 }