Populate with earthaccess.login guide in User Guide Authentications docs

[andypbarrett]

Populated authentication page in User Guide

• Populate a descriptive title. For example, instead of "Updated README.md", use a
  title such as "Add testing details to the contributor section of the README".
  Example PRs: #763

This resolves #853 add (hopefully) a complete guide to using earthaccess.login and auth methods.

The following are included in the page:

• Descriptions of how to use earthaccess.login to manually login, and use netrc and environment variables.
• Instructions to create netrc and environment variables in Linux, MacOX and Windows are included.
  • These need to be tested, especially for MacOS and Windows.
• Instructions for authenticating different endpoints; e.g. UAT.
• Instructions for retrieving S3 credentials

Much of this information comes from the "How do I" section. I suggest that we remove content from that section and use the "How do I..." to provide specific links to the User Guide Authentication.

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📚 Documentation preview 📚: https://earthaccess--862.org.readthedocs.build/en/862/

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[mfisher87]

I think a note here might be really useful -- we don't (yet) support encrypted netrc files, and this strategy of writing credentials in plain text to disk should not be used on untrusted machines or shared user accounts.

[andypbarrett]

Good suggestion. I will add an admonition

[mfisher87]

.bashrc for Linux and .profile for Mac won't always be correct. I'm not very familiar with zsh yet, but I believe it uses a .zprofile file? Bash users can permanently set envvars in .profile as well, but that will only work for "login" shells. There isn't really a one-size-fits-all answer here, it depends on the shell.

[andypbarrett]

So should we just say "add [these] to the appropriate configuration files for your operating system."

[mfisher87]

I think that makes sense as a fallback instruction; e.g.:

If you use bash and would like to set these environment variables permanently, add these two lines to your ~/.profile file: ... code ... . Otherwise, use the recommended method to persistently set environment variables for whichever shell you use.

Something like that?