fix: Set X-Requested-With header on all requests to avoid browser auth dialogs

[juliushaertl]

This used to work for most cases in the far past as jquery adds this on requests (https://github.com/jquery/jquery/blob/48cc402a917d6011c7d3e75f779f11ef91b474fb/src/ajax/xhr.js#L43-L50)

nextcloud-libraries/nextcloud-axios#637 adds this to our axios wrapper but this PR handles cases where apps or code parts are not using that.

Server has logic in place to return a dummyauth response header in case this one is set:
dfc3536

This helps to handle requests that happen in the web UI after authentication was revoked (e.g. by disabling a user) more gracefully, otherwise a request would lead to the browser showing a basic auth dialog.

Steps to reproduce:

• Login as a user
• Disable the user through occ
• Wait until the notifications app sends another request

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[artonge]

In which cases do we not use axios?

[juliushaertl]

Old code or apps that might not use our libraries, rare cases but might still happen

[skjnldsv]

/compile amend /

[juliushaertl]

/backport to stable27

[juliushaertl]

/backport to stable26

[juliushaertl]

/backport to stable25

[juliushaertl]

/backport to stable24

[backportbot-nextcloud]

The backport to stable27 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable27
git pull origin stable27

# Create the new backport branch
git checkout -b fix/foo-stable27

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts. Resolve them.
git cherry-pick abc123

# Push the cherry pick commit to the remote repository and open a pull request
git push origin fix/foo-stable27

More info at https://docs.nextcloud.com/server/latest/developer_manual/getting_started/development_process.html#manual-backport

[backportbot-nextcloud]

The backport to stable24 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable24
git pull origin stable24

# Create the new backport branch
git checkout -b fix/foo-stable24

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts. Resolve them.
git cherry-pick abc123

# Push the cherry pick commit to the remote repository and open a pull request
git push origin fix/foo-stable24

More info at https://docs.nextcloud.com/server/latest/developer_manual/getting_started/development_process.html#manual-backport

[backportbot-nextcloud]

The backport to stable26 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable26
git pull origin stable26

# Create the new backport branch
git checkout -b fix/foo-stable26

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts. Resolve them.
git cherry-pick abc123

# Push the cherry pick commit to the remote repository and open a pull request
git push origin fix/foo-stable26

More info at https://docs.nextcloud.com/server/latest/developer_manual/getting_started/development_process.html#manual-backport

[backportbot-nextcloud]

The backport to stable25 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable25
git pull origin stable25

# Create the new backport branch
git checkout -b fix/foo-stable25

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts. Resolve them.
git cherry-pick abc123

# Push the cherry pick commit to the remote repository and open a pull request
git push origin fix/foo-stable25

More info at https://docs.nextcloud.com/server/latest/developer_manual/getting_started/development_process.html#manual-backport