> For a complete page index, fetch https://developer.close.com/llms.txt

# Authentication with OAuth

To implement authentication with OAuth 2.0, you need to [create an OAuth app](/integrations/create-an-oauth-app) to get your **Client ID** and **Client Secret**.

You'll also need to implement a redirect URI in your application. In the examples below we use `https://example.com/callback/close` as that redirect URI.

## Authorization

First you need to have your application redirect the user to Close's
authorization page with the `client_id` and `redirect_uri`.

```
https://app.close.com/oauth2/authorize/?client_id=CLIENT_ID&response_type=code
```

The user will be presented with a Consent Screen and be able to select an
organization and grant or decline access. If the user chooses to grant access,
their browser is redirected to that OAuth App's `redirect_uri`, the
Authorization Code is passed inside the `code` query parameter.

```
https://example.com/callback/close?code=CODE
```

If the users chooses to decline access instead, their browser is redirected to
the same `redirect_uri` with error information in query parameters.

```
https://example.com/callback/close?error=access_denied
```

## Obtain Access Token

The Authorization Code can be exchanged for an Access Token by performing a POST
request with form-encoded parameters to `https://api.close.com/oauth2/token/`

```
POST /oauth2/token/ HTTP/1.1
Content-Type: application/x-www-form-urlencoded
Host: api.close.com

client_id=CLIENT_ID&client_secret=CLIENT_SECRET&grant_type=authorization_code&code=CODE
```

You will get a following JSON response:

```json
{
  "token_type": "Bearer",
  "access_token": "ACCESS_TOKEN",
  "expires_in": 3600,
  "refresh_token": "REFRESH_TOKEN",
  "scope": "all.full_access offline_access",
  "organization_id": "ORGANIZATION_ID",
  "user_id": "USER_ID"
}
```

Notice that the Access Token has a limited lifetime and expires in `expires_in`
seconds from the moment it was issued. If your application has `offline_access`
scope `refresh_token` property will be present in the response and you can
refresh Access Token (See below).

## Perform API calls with Access Token

Send your HTTP requests with an `Authorization` header that contains the word
`Bearer` followed by a space and the Access Token.

e.g. using cURL:

```bash
curl https://api.close.com/api/v1/me/ -H "Authorization: Bearer ACCESS_TOKEN"
```

which results in the following request:

```
GET /api/v1/me/ HTTP/1.1
Authorization: Bearer ACCESS_TOKEN
Host: api.close.com
```

## Refresh Access Token

If your application has an `offline_access` scope you can refresh the Access
Token using Refresh Token obtained before by performing a POST request with
form-encoded parameters to `https://api.close.com/oauth2/token/`

```
POST /oauth2/token/ HTTP/1.1
Content-Type: application/x-www-form-urlencoded
Host: api.close.com

client_id=CLIENT_ID&client_secret=CLIENT_SECRET&grant_type=refresh_token&refresh_token=REFRESH_TOKEN
```

You will get a following JSON response

```json
{
  "token_type": "Bearer",
  "access_token": "ACCESS_TOKEN",
  "expires_in": 3600,
  "refresh_token": "REFRESH_TOKEN",
  "scope": "all.full_access offline_access",
  "organization_id": "ORGANIZATION_ID",
  "user_id": "USER_ID"
}
```

Note that the authorization server issues a new Refresh Token and the client
must discard the old Refresh Token and replace it with the new one. The
authorization server revokes the old Refresh Token after issuing a new one.

## Revoke application access

It's a good security practice to revoke Access and Refresh Tokens immediately if
the user chooses to disable the integration with Close. You can accomplish this
by performing a POST request with form-encoded parameters to
`https://api.close.com/oauth2/revoke/`.

```
POST /oauth2/revoke/ HTTP/1.1
Content-Type: application/x-www-form-urlencoded
Host: api.close.com

client_id=CLIENT_ID&client_secret=CLIENT_SECRET&token=REFRESH_TOKEN
```

> How to register an OAuth 2.0 application and authenticate users with the Close API.