See this page if you are using a self signed cert.

1. Login to your Firefly instance
2. Click on Options, then profile
3. Scroll down to OAuth Clients section and click on Create New Client
4. Use any name and ensure you are using http:https://empty as your redirect URL.

5. Click Save Changes
6. Copy the client secret that you have just created

7. Paste it into the mobile app login screen under secret field

Click sign in and you will be bought to your Firefly III instance. Complete the sign in process.

For Chromium based browsers, you will be redirected back to the app once authentication is successful.

For Firefox and it's derivatives(Fennec / Firefox focus), there is an extra step. Once authentication is completed, you will be shown a Server not found error message. Click on refresh and then click on the Android icon in the address bar, you will be redirected back to the app.

For FOSS Browser, the steps are somewhat similar to Firefox.

1. Click on the notification that pops up

2. You will be shown a ERR_NAME_NOT_RESOLVED error message. Click on the overflow menu button

3. Click on share button and Open link with ...

1. Scroll down to Personal Access Tokens(below OAuth Clients)
2. Give it any name, it does not matter.
3. Click on create
4. Copy the content of the text box

5. Paste it into the app