Refresh access_token via refresh_token in Keycloak

@maslick is correct you have to supply the client secret too, no need for authorization header in this case:

http://localhost:8080/auth/realms/{realm}/protocol/openid-connect/token

In case of expired refresh token it returns:

If you don't add the secret you get 401 unauthorized even though the refresh token is correct

keycloak has REST API for creating an access_token using refresh_token. It is a POST endpoint with application/x-www-form-urlencoded

Here is how it looks:

Method: POST
URL: https://keycloak.example.com/auth/realms/myrealm/protocol/openid-connect/token
Body type: x-www-form-urlencoded
Form fields:    
client_id : <my-client-name>
grant_type : refresh_token
refresh_token: <my-refresh-token>

This will give you new access token using refresh token.

NOTE: if your refresh token is expired it will throw 400 exception in that you can make user login again.

Check out a sample in Postman, you can develop and corresponding API using this.