feat(core): enable sending client credentials in body (#4377)

* ⚡ Enable inject credentials in the body for OAuth2 CC

* 🐛 Persist token data

* 👕 Fix linting error

packages/core/src/NodeExecuteFunctions.ts

@@ -102,6 +102,7 @@ import {
 	PLACEHOLDER_EMPTY_EXECUTION_ID,
 } from '.';
 import { extractValue } from './ExtractValue';
+import { getClientCredentialsToken } from './OAuth2Helper';
 
 axios.defaults.timeout = 300000;
 // Prevent axios from adding x-form-www-urlencoded headers by default
@@ -933,9 +934,10 @@ export async function requestOAuth2(
 	});
 
 	let oauthTokenData = credentials.oauthTokenData as clientOAuth2.Data;
+
 	// if it's the first time using the credentials, get the access token and save it into the DB.
 	if (credentials.grantType === OAuth2GrantType.clientCredentials && oauthTokenData === undefined) {
-		const { data } = await oAuthClient.credentials.getToken();
+		const { data } = await getClientCredentialsToken(oAuthClient, credentials);
 
 		// Find the credentials
 		if (!node.credentials?.[credentialsType]) {
@@ -950,7 +952,7 @@ export async function requestOAuth2(
 		await additionalData.credentialsHelper.updateCredentials(
 			nodeCredentials,
 			credentialsType,
-			credentials as unknown as ICredentialDataDecryptedObject,
+			Object.assign(credentials, { oauthTokenData: data }),
 		);
 
 		oauthTokenData = data;
@@ -1005,7 +1007,7 @@ export async function requestOAuth2(
 				// if it's OAuth2 with client credentials grant type, get a new token
 				// instead of refreshing it.
 				if (OAuth2GrantType.clientCredentials === credentials.grantType) {
-					newToken = await token.client.credentials.getToken();
+					newToken = await getClientCredentialsToken(token.client, credentials);
 				} else {
 					newToken = await token.refresh(tokenRefreshOptions);
 				}
@@ -1073,7 +1075,7 @@ export async function requestOAuth2(
 			// if it's OAuth2 with client credentials grant type, get a new token
 			// instead of refreshing it.
 			if (OAuth2GrantType.clientCredentials === credentials.grantType) {
-				newToken = await token.client.credentials.getToken();
+				newToken = await getClientCredentialsToken(token.client, credentials);
 			} else {
 				newToken = await token.refresh(tokenRefreshOptions);
 			}

packages/core/src/OAuth2Helper.ts

@@ -0,0 +1,22 @@
+/* eslint-disable @typescript-eslint/naming-convention */
+import { ICredentialDataDecryptedObject } from 'n8n-workflow';
+import clientOAuth2 from 'client-oauth2';
+
+export const getClientCredentialsToken = async (
+	oAuth2Client: clientOAuth2,
+	credentials: ICredentialDataDecryptedObject,
+): Promise<clientOAuth2.Token> => {
+	const options = {};
+	if (credentials.authentication === 'body') {
+		Object.assign(options, {
+			headers: {
+				Authorization: '',
+			},
+			body: {
+				client_id: credentials.clientId as string,
+				client_secret: credentials.clientSecret as string,
+			},
+		});
+	}
+	return oAuth2Client.credentials.getToken(options);
+};

packages/nodes-base/credentials/OAuth2Api.credentials.ts

@@ -82,11 +82,6 @@ export class OAuth2Api implements ICredentialType {
 			displayName: 'Authentication',
 			name: 'authentication',
 			type: 'options',
-			displayOptions: {
-				show: {
-					grantType: ['authorizationCode'],
-				},
-			},
 			options: [
 				{
 					name: 'Body',