How do I configure a network interface bridge from WiFi to Ethernet with Debian?

For configuring a bridge from ethernet to wifi, it is as simple as doing in your /etc/network/interfaces:

auto eth0
allow-hotplug eth0
iface eth0 inet manual

auto wlan0
allow-hotplug wlan0
iface wlan0 inet manual

auto br0
iface br0 inet static
bridge_ports eth0 wlan0
    address 192.168.1.100
    netmask 255.255.255.0

Replace the IP address with something more appropriate to your network.

If you prefer the IP attribution done via DHCP, change it to:

auto br0
iface br0 inet dhcp
bridge_ports eth0 wlan0

After changing /etc/network/interfaces, either restarting Debian or doing

service networking restart

Will activate this configuration.

You will have to make sure for this configuration to have bridge-utils installed. You can install it with:

sudo apt install bridge-utils

For more information, see:

BRIDGE-UTILS-INTERFACES

The wlan0 interface also has to be condigured to connect to your remote AP so this configuration is not be used verbatim.

Additional note: bridging eth0 and wlan0 together means in poor layman´s terms that br0 will present itself as a single logical interface englobing the interfaces that make part of the bridge. Usually such configuration is made when both extend or belong to the same network.