Migrate IGDB v3 API to v4 for games command
## Description
<!-- Describe the bug you've found -->
IGDB shut down APIv3 in October 2020. `games` command is currently built to use v3 of API, but now, when URLs is gone, this command is currently not usable. Command must be migrated APIv4, about to what migrating can be read https://api-docs.igdb.com/#upgrading-to-v4-from-v3.

## Steps to Reproduce
<!-- Detail the exact list of steps to be able to encounter the bug -->
When you have API key of IGDB, then genres refreshing task fails, because API not found, also command fails.

## Expected Behaviour
<!-- Outline what you expect to occur, include screenshots if relevant -->
Should successfully refresh genres and run commands.

## Actual Behaviour
<!-- Outline what occurs instead of the expected behaviour, include screenshots if relevant -->
Genres refreshing and command is failing.

## Known Impacted Platforms
<!-- Replace [ ] with [x] to mark items -->

- [x] Web
- [x] Desktop
- [x] Android App
- [x] iOS App

## Possible Solutions
<!-- Detail any solutions you might have in mind to be able to resolve the bug -->
Only way is migrating from APIv3 to APIv4.


## Would you like to implement a fix?

***Note: For high-priority or critical bugs, fixes may be implemented by staff.***
<!-- Replace [ ] with [x] with your choice -->

- [ ] I'd like to implement the bug fix
- [x] Anyone can implement the bug fix

diff --git a/bot/constants.py b/bot/constants.py
index 24765c2a..d63a063e 100644
--- a/bot/constants.py
+++ b/bot/constants.py
@@ -241,7 +241,8 @@ class Tokens(NamedTuple):
     youtube = environ.get("YOUTUBE_API_KEY")
     tmdb = environ.get("TMDB_API_KEY")
     nasa = environ.get("NASA_API_KEY")
-    igdb = environ.get("IGDB_API_KEY")
+    igdb_client_id = environ.get("IGDB_CLIENT_ID")
+    igdb_client_secret = environ.get("IGDB_CLIENT_SECRET")
     github = environ.get("GITHUB_TOKEN")
 
 
diff --git a/bot/exts/evergreen/game.py b/bot/exts/evergreen/game.py
index d0fd7a40..d37be0e2 100644
--- a/bot/exts/evergreen/game.py
+++ b/bot/exts/evergreen/game.py
@@ -2,7 +2,8 @@ import difflib
 import logging
 import random
 import re
-from datetime import datetime as dt
+from asyncio import sleep
+from datetime import datetime as dt, timedelta
 from enum import IntEnum
 from typing import Any, Dict, List, Optional, Tuple
 
@@ -17,10 +18,25 @@ from bot.utils.decorators import with_role
 from bot.utils.pagination import ImagePaginator, LinePaginator
 
 # Base URL of IGDB API
-BASE_URL = "https://api-v3.igdb.com"
+BASE_URL = "https://api.igdb.com/v4"
 
-HEADERS = {
-    "user-key": Tokens.igdb,
+CLIENT_ID = Tokens.igdb_client_id
+CLIENT_SECRET = Tokens.igdb_client_secret
+
+# The number of seconds before expiry that we attempt to re-fetch a new access token
+ACCESS_TOKEN_RENEWAL_WINDOW = 60*60*24*2
+
+# URL to request API access token
+OAUTH_URL = "https://id.twitch.tv/oauth2/token"
+
+OAUTH_PARAMS = {
+    "client_id": CLIENT_ID,
+    "client_secret": CLIENT_SECRET,
+    "grant_type": "client_credentials"
+}
+
+BASE_HEADERS = {
+    "Client-ID": CLIENT_ID,
     "Accept": "application/json"
 }
 
@@ -135,8 +151,47 @@ class Games(Cog):
         self.http_session: ClientSession = bot.http_session
 
         self.genres: Dict[str, int] = {}
-
-        self.refresh_genres_task.start()
+        self.headers = BASE_HEADERS
+
+        self.bot.loop.create_task(self.renew_access_token())
+
+    async def renew_access_token(self) -> None:
+        """Refeshes V4 access token a number of seconds before expiry. See `ACCESS_TOKEN_RENEWAL_WINDOW`."""
+        while True:
+            async with self.http_session.post(OAUTH_URL, params=OAUTH_PARAMS) as resp:
+                result = await resp.json()
+                if resp.status != 200:
+                    # If there is a valid access token continue to use that,
+                    # otherwise unload cog.
+                    if "Authorization" in self.headers:
+                        time_delta = timedelta(seconds=ACCESS_TOKEN_RENEWAL_WINDOW)
+                        logger.error(
+                            "Failed to renew IGDB access token. "
+                            f"Current token will last for {time_delta} "
+                            f"OAuth response message: {result['message']}"
+                        )
+                    else:
+                        logger.warning(
+                            "Invalid OAuth credentials. Unloading Games cog. "
+                            f"OAuth response message: {result['message']}"
+                        )
+                        self.bot.remove_cog('Games')
+
+                    return
+
+            self.headers["Authorization"] = f"Bearer {result['access_token']}"
+
+            # Attempt to renew before the token expires
+            next_renewal = result["expires_in"] - ACCESS_TOKEN_RENEWAL_WINDOW
+
+            time_delta = timedelta(seconds=next_renewal)
+            logger.info(f"Successfully renewed access token. Refreshing again in {time_delta}")
+
+            # This will be true the first time this loop runs.
+            # Since we now have an access token, its safe to start this task.
+            if self.genres == {}:
+                self.refresh_genres_task.start()
+            await sleep(next_renewal)
 
     @tasks.loop(hours=24.0)
     async def refresh_genres_task(self) -> None:
@@ -156,9 +211,8 @@ class Games(Cog):
     async def _get_genres(self) -> None:
         """Create genres variable for games command."""
         body = "fields name; limit 100;"
-        async with self.http_session.get(f"{BASE_URL}/genres", data=body, headers=HEADERS) as resp:
+        async with self.http_session.post(f"{BASE_URL}/genres", data=body, headers=self.headers) as resp:
             result = await resp.json()
-
         genres = {genre["name"].capitalize(): genre["id"] for genre in result}
 
         # Replace complex names with names from ALIASES
@@ -306,7 +360,7 @@ class Games(Cog):
         body = GAMES_LIST_BODY.format(**params)
 
         # Do request to IGDB API, create headers, URL, define body, return result
-        async with self.http_session.get(url=f"{BASE_URL}/games", data=body, headers=HEADERS) as resp:
+        async with self.http_session.post(url=f"{BASE_URL}/games", data=body, headers=self.headers) as resp:
             return await resp.json()
 
     async def create_page(self, data: Dict[str, Any]) -> Tuple[str, str]:
@@ -348,7 +402,7 @@ class Games(Cog):
         # Define request body of IGDB API request and do request
         body = SEARCH_BODY.format(**{"term": search_term})
 
-        async with self.http_session.get(url=f"{BASE_URL}/games", data=body, headers=HEADERS) as resp:
+        async with self.http_session.post(url=f"{BASE_URL}/games", data=body, headers=self.headers) as resp:
             data = await resp.json()
 
         # Loop over games, format them to good format, make line and append this to total lines
@@ -377,7 +431,7 @@ class Games(Cog):
             "offset": offset
         })
 
-        async with self.http_session.get(url=f"{BASE_URL}/companies", data=body, headers=HEADERS) as resp:
+        async with self.http_session.post(url=f"{BASE_URL}/companies", data=body, headers=self.headers) as resp:
             return await resp.json()
 
     async def create_company_page(self, data: Dict[str, Any]) -> Tuple[str, str]:
@@ -418,7 +472,10 @@ class Games(Cog):
 def setup(bot: Bot) -> None:
     """Add/Load Games cog."""
     # Check does IGDB API key exist, if not, log warning and don't load cog
-    if not Tokens.igdb:
-        logger.warning("No IGDB API key. Not loading Games cog.")
+    if not Tokens.igdb_client_id:
+        logger.warning("No IGDB client ID. Not loading Games cog.")
+        return
+    if not Tokens.igdb_client_secret:
+        logger.warning("No IGDB client secret. Not loading Games cog.")
         return
     bot.add_cog(Games(bot))
['bot/constants.py', 'bot/exts/evergreen/game.py']