impl: models for dynamic client registration

OAuth allows programatic client registration for apps like Coder Toolbox
via the DCR endpoint which requires a name for the client app, the requested
scopes, redirect URI, etc... DCR replies back with a similar structure but
in addition it returs two very important properties: client_id - a unique
client identifier string and also a client_secret - a secret string value
used by clients to authenticate to the token endpoint.

Author: fioan89

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

@@ -0,0 +1,14 @@
+package com.coder.toolbox.oauth
+
+import com.squareup.moshi.Json
+import com.squareup.moshi.JsonClass
+
+@JsonClass(generateAdapter = true)
+data class ClientRegistrationRequest(
+    @field:Json(name = "client_name") val clientName: String,
+    @field:Json(name = "redirect_uris") val redirectUris: List<String>,
+    @field:Json(name = "grant_types") val grantTypes: List<String>,
+    @field:Json(name = "response_types") val responseTypes: List<String>,
+    @field:Json(name = "scope") val scope: String,
+    @field:Json(name = "token_endpoint_auth_method") val tokenEndpointAuthMethod: String? = null
+)

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

@@ -0,0 +1,21 @@
+package com.coder.toolbox.oauth
+
+import com.squareup.moshi.Json
+import com.squareup.moshi.JsonClass
+
+/**
+ * DCR response
+ */
+@JsonClass(generateAdapter = true)
+data class ClientRegistrationResponse(
+    @field:Json(name = "client_id") val clientId: String,
+    @field:Json(name = "client_secret") val clientSecret: String,
+    @field:Json(name = "client_name") val clientName: String,
+    @field:Json(name = "redirect_uris") val redirectUris: List<String>,
+    @field:Json(name = "grant_types") val grantTypes: List<String>,
+    @field:Json(name = "response_types") val responseTypes: List<String>,
+    @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?
+)