OauthTokenService (LTI Launch 1.4.6 API)

```
public interface OauthTokenService
```
A service to be implemented and supplied as an autowire candidate by any consumers of this library

Author:

alexanda, ssnelson

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`String`	`getRefreshToken(String userId)`	Fetch the refresh token from whatever persistence solution the consumer is currently using
`String`	`storeToken(String userId, String refreshToken)`	Stores a new refresh token in whatever persistence solution the consumer is using
`String`	`updateToken(String userId, String refreshToken)`	Updates the refresh token saved in the data source for a given user Should only be called on very specific situations, however it is necessary

- Method Detail
  - getRefreshToken
```
String getRefreshToken(String userId)
```
    Fetch the refresh token from whatever persistence solution the consumer is currently using
    
    Parameters:
    
    userId - The userId the refresh token needs to belong to
    
    Returns:
    
    Refresh token to be used to get new API tokens, as a string
  - storeToken
```
String storeToken(String userId,
                  String refreshToken)
```
    Stores a new refresh token in whatever persistence solution the consumer is using
    
    Parameters:
    
    userId - The userId the refresh token belongs to
    
    refreshToken - The refresh token to be saved
    
    Returns:
    
    Same refresh token passed in the refreshToken parameter
  - updateToken
```
String updateToken(String userId,
                   String refreshToken)
```
    Updates the refresh token saved in the data source for a given user Should only be called on very specific situations, however it is necessary
    
    Parameters:
    
    userId - The userId the refresh token belongs to
    
    refreshToken - The refresh token to be saved
    
    Returns:
    
    Same refresh token passed in the refreshToken parameter