How to fix remote: Invalid username or password. fatal: Authentication failed in Git

Since password authentication is deprecated, you need to create a Personal Access Token. Here's how for major providers:

GitHub:
1. Go to [github.com/settings/tokens](https://github.com/settings/tokens)
2. Click "Generate new token" > "Generate new token (classic)"
3. Enter a description (e.g., "Git CLI access")
4. Select expiration (or "No expiration" for CI/CD)
5. Select scopes: at minimum check repo for private repositories
6. Click "Generate token"
7. Copy the token immediately - you won't be able to see it again!

GitLab:
1. Go to gitlab.com/-/user_settings/personal_access_tokens
2. Enter a name and optional expiration date
3. Select scopes: read_repository, write_repository for git operations
4. Click "Create personal access token"
5. Copy the token

Bitbucket:
1. Go to bitbucket.org/account/settings/app-passwords
2. Click "Create app password"
3. Enter a label and select permissions
4. Copy the generated password

Old credentials may be stored in your system's credential manager. Clear them before entering new ones:

Windows (Credential Manager):

# Open Credential Manager
control /name Microsoft.CredentialManager

# Or via command line - remove git credentials
cmdkey /delete:git:https://github.com

Look under "Windows Credentials" for entries containing github.com, gitlab.com, or bitbucket.org and remove them.

macOS (Keychain):

# Remove GitHub credentials from Keychain
git credential-osxkeychain erase
host=github.com
protocol=https
# Press Enter twice after the above lines

# Or open Keychain Access app and search for "github.com"

Linux:

# If using Git Credential Manager
git credential reject
host=github.com
protocol=https
# Press Enter twice

# If using .git-credentials file
# Edit or remove ~/.git-credentials

# If using GNOME Keyring
secret-tool clear server github.com

Now use your Personal Access Token instead of your password:

# When prompted for password, enter your PAT instead
git push origin main
Username: your-username
Password: <paste your Personal Access Token here>

Store credentials so you don't have to enter them every time:

# Enable credential caching (stores in memory for 15 minutes)
git config --global credential.helper cache

# Or store permanently (less secure but convenient)
git config --global credential.helper store

# On macOS, use Keychain
git config --global credential.helper osxkeychain

# On Windows, use Credential Manager
git config --global credential.helper wincred
# Or the newer manager-core
git config --global credential.helper manager-core

Then run any git command that requires authentication - you'll be prompted once, and credentials will be saved.

You can embed the token directly in the remote URL (useful for CI/CD, but be careful with security):

# View current remote URL
git remote -v

# Update remote URL to include token
git remote set-url origin https://<USERNAME>:<TOKEN>@github.com/<USERNAME>/<REPO>.git

# Example
git remote set-url origin https://johndoe:[email protected]/johndoe/my-repo.git

Warning: This stores your token in plain text in .git/config. For shared machines or public repos, prefer credential helpers or SSH keys.

For CI/CD pipelines, use environment variables:

git remote set-url origin https://${GIT_USER}:${GIT_TOKEN}@github.com/${GIT_USER}/${REPO}.git

SSH keys are more secure and don't expire like tokens. Here's how to set them up:

Generate an SSH key:

# Generate new SSH key
ssh-keygen -t ed25519 -C "[email protected]"

# Start SSH agent
eval "$(ssh-agent -s)"

# Add key to agent
ssh-add ~/.ssh/id_ed25519

Add the public key to your Git provider:

# Copy public key to clipboard
cat ~/.ssh/id_ed25519.pub
# Copy the output

- GitHub: Settings > SSH and GPG keys > New SSH key
- GitLab: Preferences > SSH Keys > Add key
- Bitbucket: Personal settings > SSH keys > Add key

Update your remote URL to use SSH:

# Change from HTTPS to SSH
git remote set-url origin [email protected]:username/repository.git

# Verify the change
git remote -v

# Test SSH connection
ssh -T [email protected]

Make sure you're using your username, not your email address:

# Check current Git username configuration
git config --global user.name

# Check what Git is sending to the remote
GIT_CURL_VERBOSE=1 git fetch 2>&1 | grep -i "user"

Find your username:
- GitHub: github.com > Profile icon > Your profile (username is in URL)
- GitLab: gitlab.com > Profile icon > Edit profile
- Bitbucket: bitbucket.org > Personal settings > Account settings

Note: Usernames are often case-sensitive in Git operations. If your username is "JohnDoe", use exactly that, not "johndoe".