Where can I find current authoritative information about COVID-19 related travel bans to the US?

Here is a link to the full text of the proclamation issued by Trump. The countries affected are those in the Schengen area, and this applies to anyone who has been in any Schengen country in the last 14 days, so even if your flights arrives from somewhere else, it would apply, for example.

For purposes of this proclamation, the Schengen Area comprises 26 European states: Austria, Belgium, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Italy, Latvia, Liechtenstein, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, and Switzerland.

I will quote the meat of it below, which goes mostly over which persons are affected, and what the exceptions are:

Section 1. Suspension and Limitation on Entry. The entry into the United States, as immigrants or nonimmigrants, of all aliens who were physically present within the Schengen Area during the 14-day period preceding their entry or attempted entry into the United States is hereby suspended and limited subject to section 2 of this proclamation.

Sec. 2. Scope of Suspension and Limitation on Entry.

(a) Section 1 of this proclamation shall not apply to:

(i) any lawful permanent resident of the United States;

(ii) any alien who is the spouse of a U.S. citizen or lawful permanent resident;

(iii) any alien who is the parent or legal guardian of a U.S. citizen or lawful permanent resident, provided that the U.S. citizen or lawful permanent resident is unmarried and under the age of 21;

(iv) any alien who is the sibling of a U.S. citizen or lawful permanent resident, provided that both are unmarried and under the age of 21;

(v) any alien who is the child, foster child, or ward of a U.S. citizen or lawful permanent resident, or who is a prospective adoptee seeking to enter the United States pursuant to the IR-4 or IH-4 visa classifications;

(vi) any alien traveling at the invitation of the United States Government for a purpose related to containment or mitigation of the virus;

(vii) any alien traveling as a nonimmigrant pursuant to a C-1, D, or C-1/D nonimmigrant visa as a crewmember or any alien otherwise traveling to the United States as air or sea crew;

(viii) any alien

(A) seeking entry into or transiting the United States pursuant to one of the following visas: A-1, A-2, C-2, C-3 (as a foreign government official or immediate family member of an official), E-1 (as an employee of TECRO or TECO or the employee's immediate family members), G-1, G-2, G-3, G-4, NATO-1 through NATO-4, or NATO-6 (or seeking to enter as a nonimmigrant in one of those NATO categories); or

(B) whose travel falls within the scope of section 11 of the United Nations Headquarters Agreement;

(ix) any alien whose entry would not pose a significant risk of introducing, transmitting, or spreading the virus, as determined by the Secretary of Health and Human Services, through the CDC Director or his designee;

(x) any alien whose entry would further important United States law enforcement objectives, as determined by the Secretary of State, the Secretary of Homeland Security, or their respective designees, based on a recommendation of the Attorney General or his designee;

(xi) any alien whose entry would be in the national interest, as determined by the Secretary of State, the Secretary of Homeland Security, or their designees; or

(xii) members of the U.S. Armed Forces and spouses and children of members of the U.S. Armed Forces.

(b) Nothing in this proclamation shall be construed to affect any individual's eligibility for asylum, withholding of removal, or protection under the regulations issued pursuant to the legislation implementing the Convention Against Torture and Other Cruel, Inhuman or Degrading Treatment or Punishment, consistent with the laws and regulations of the United States.

Sec. 3. Implementation and Enforcement. (a) The Secretary of State shall implement this proclamation as it applies to visas pursuant to such procedures as the Secretary of State, in consultation with the Secretary of Homeland Security, may establish. The Secretary of Homeland Security shall implement this proclamation as it applies to the entry of aliens pursuant to such procedures as the Secretary of Homeland Security, in consultation with the Secretary of State, may establish.

(b) Consistent with applicable law, the Secretary of State, the Secretary of Transportation, and the Secretary of Homeland Security shall ensure that any alien subject to this proclamation does not board an aircraft traveling to the United States.

(c) The Secretary of Homeland Security may establish standards and procedures to ensure the application of this proclamation at and between all United States ports of entry.

(d) An alien who circumvents the application of this proclamation through fraud, willful misrepresentation of a material fact, or illegal entry shall be a priority for removal by the Department of Homeland Security.

Sec. 4. Termination. This proclamation shall remain in effect until terminated by the President. The Secretary of Health and Human Services shall recommend that the President continue, modify, or terminate this proclamation as described in section 5 of Proclamation 9984, as amended.

Sec. 5. Effective Date. This proclamation is effective at 11:59 p.m. eastern daylight time on March 13, 2020. This proclamation does not apply to persons aboard a flight scheduled to arrive in the United States that departed prior to 11:59 p.m. eastern daylight time on March 13, 2020.

Sec. 6. Severability. It is the policy of the United States to enforce this proclamation to the maximum extent possible to advance the national security, public safety, and foreign policy interests of the United States. Accordingly:

(a) if any provision of this proclamation, or the application of any provision to any person or circumstance, is held to be invalid, the remainder of this proclamation and the application of its provisions to any other persons or circumstances shall not be affected thereby; and

(b) if any provision of this proclamation, or the application of any provision to any person or circumstance, is held to be invalid because of the lack of certain procedural requirements, the relevant executive branch officials shall implement those procedural requirements to conform with existing law and with any applicable court orders.

Sec. 7. General Provisions. (a) Nothing in this proclamation shall be construed to impair or otherwise affect:

(i) the authority granted by law to an executive department or agency, or the head thereof; or

(ii) the functions of the Director of the Office of Management and Budget relating to budgetary, administrative, or legislative proposals.

(b) This proclamation shall be implemented consistent with applicable law and subject to the availability of appropriations.

(c) This proclamation is not intended to, and does not, create any right or benefit, substantive or procedural, enforceable at law or in equity by any party against the United States, its departments, agencies, or entities, its officers, employees, or agents, or any other person.