> For the complete documentation index, see [llms.txt](https://apidocs.arionbanki.is/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://apidocs.arionbanki.is/psd2/more-information/redirection-methods.md).

# Redirection methods

There are two ways to redirect the user for strong customer authentication (SCA). 

* App-to-app
* Web browser

## App-to-app

This is the preferred way of redirection as it uses a customer flow which payment users are accostomed to. The app-to-app redirection uses the Arion app to autherize payment initiation and account information service requests.

### Instructions for app-to-app redirection

1. The app redirection URI needs to be listed on your application on the Developer Portal.
2. There are two parameters that decide how the user are redirected for authorization: `TPP-Redirect-Preferred` and `TPP-Redirect-URI` . These parameters are set when creating a payment initiation request or a account information service consent request. 
   * `TPP-Redirect-Preferred` 
     * For the app-to-app flow, this parameter should be set to "false"
   * `TPP-Redirect-URI` 
     * App URI of the TPP, where the transaction flow shall be redirected to after a redirect.
   * The chosen approach will be indicated with the response header `ASPSP-SCA-Approach`.

## Web browser

This option not preferred as it uses an older and more complicated user flow. This option will likely be depricated in the future. However, as this was the first option that was introduced and it currently has TPP connections that rely on this flow, this is currently the default redirect option if none is chosen. 

### Instructions for web browser redirection

1. The TPP's redirection URI needs to be listed on your application on the Developer Portal.
2. There are two parameters that decide how the user are redirected for authorization: `TPP-Redirect-Preferred` and `TPP-Redirect-URI` . These parameters are set when creating a payment initiation request or a account information service consent request. 
   * `TPP-Redirect-Preferred` 
     * For the web browser flow, this parameter should be set to "true" (this is the default value).
   * `TPP-Redirect-URI` 
     * URI of the TPP, where the transaction flow shall be redirected to after a redirect.
   * The chosen approach will be indicated with the response header `ASPSP-SCA-Approach`.